In the build-up to this fixture, Emma Hayes had declared it a meeting of the ‘experienced champions versus the ambitious, hungry challengers’, and her players showed plenty of nous to get their way past a side who had stunned everyone to lead the WSL standings.

We flew out of the blocks and could have had a hatful of early goals, with Sam Kerr unable to make the most of four clear opportunities, but we made our attacking dominance pay after half an hour when Harder bundled the ball home at the end of a penalty-box scramble.

Just as they had done on the opening weekend of the season, when the two sides previously met, United drew level in the second half. On this occasion it was a wonderful strike by Lauren James, whose brother Reece stars for our men’s team, as she came off the bench to net the equaliser only five minutes after coming on.

The response from the Blues is exactly what one would expect from the champions, however, and while there was nothing pretty about the build-up, as a long punt up field by Ann-Katrin Berger was met by Kirby, the finish from our No14 was exceptional. After netting four last weekend against Reading, Super Fran is clearly intent on making 2021 a year to remember.

Although there was another near miss from James, who fired wide with her left foot from inside the box, we saw out the victory with the minimum of fuss and the three points ensured we overtook our opponents at the top of the table, thanks to our superior goal difference. We also have a game in hand.

A fifth straight league win also took us to 31 matches unbeaten in the WSL, which equals the mark set by Manchester City, with our last defeat in the competition coming against Birmingham City on 27 January 2019.

We’ll have a chance to set a new record next Sunday when we travel to Bristol City, who are managed by former Chelsea manager Matt Beard. Before then, however, is the small matter of a Continental League Cup quarter-final against Man City on Wednesday evening, as we look to continue our defence of the trophy we won last February.

After a rare midweek without a fixture, Hayes had a full week to prepare for this game following last Sunday’s 5-0 win at Reading. The Blues boss made four changes to her starting line-up, bringing in Maren Mjelde, Magdalena Eriksson, Ji So-Yun and Harder, as Hannah Blundell, Sophie Ingle, Niamh Charles and Guro Reiten dropped to the bench.

We lined up with Berger in goal, as Mjelde and Eriksson were reunited with Millie Bright and Jonna Andersson in what has been our most common back four this season. Ji resumed her flourishing partnership with Melanie Leupolz in midfield, behind the trio of Kirby, Harder and Erin Cuthbert, who offered plenty of support for lone forward Kerr.

In her interview with BT Sport ahead of kick-off, Hayes promised entertainment and both sides wasted little time delivering on that. United’s high press led to an interception deep in Chelsea territory, which required a well-timed intervention from the returning Eriksson, but the Blues responded with a pair of gilt-edged chances for Kerr inside four minutes.

The first was of the Australian’s own making, as she picked up the ball midway inside the Red Devils’ half and embarked on a barnstorming run, skipping past two challenges and then drilling a low strike that Mary Earps kept out with her feet. Soon after she was presented with an even better opportunity, as Kirby won the ball back and sent Kerr away down the left, but her finish was just the wrong side of the near post.

The game was being played at a relentless pace and though United looked to be holding their own, the clearer chances were being fashioned by Chelsea. On 12 minutes we cut through their defence once again through Kerr, as she showed for the ball, laid it off to Cuthbert and immediately ran in behind her marker. The pass back to her was inch perfect and our No20 unselfishly squared for Kirby, but it was just slightly overhit and the opportunity went begging.

Incredibly, the visitors fell for the same move moments later, this time with Kirby playing the ball through for Kerr, and the Australian went for goal herself with a prodded finish that missed the target. It was no exaggeration to say we could have been 4-0 up inside the first quarter of an hour, and the Manchester United boss Casey Stoney, a former Chelsea defender, cut a furious figure in the visiting dugout.

For all their frailty in their own half, the Red Devils looked sharp in attack and there were a few relieved players wearing blue after Christen Press fired wide after a cross was only half-cleared to her on the edge of the box.

However, just as they looked to have got a foothold in the game, the opening goal duly arrived at the other end of the pitch, as our pressure finally told. The Blues won a corner when Kirby, having been played in by a smart pass from Mjelde, tried to catch out Earps at the near post and the keeper made a smart stop.

From the resulting corner, there was chaos: Eriksson’s header was cleared off the line, Kirby smashed a half-volley that looked destined for the far corner, only to come back off the post, and, finally, Harder reacted quickest to force the ball home through a crowded six-yard box. Clearly inspired by James Maddison on Saturday evening, the Dane went for her own socially distanced celebration, much to the delight of her team-mates.

The goal came from our eighth shot of the half and it meant we had now scored in 20 home WSL games in a row, a run which dates back to October 2018, but it also prompted United’s best spell of the half as they came back into it in the final quarter of an hour. As well as enjoying more possession, they also created a few chances of their own, one of which was for Hanson. The winger got in behind and knocked the ball past Berger before rolling it into an empty net, but a raised flag for offside quickly swiftly curtailed her celebration.

That proved to be the last meaningful action of what had been an action-packed opening half. Could the second half live up to such high standards?

Although neither manager made a change at the interval, it didn’t take long for Stoney to intervene, as she introduced a player with her own Chelsea connection in James, who was brought on in place of Press, tasked with getting the visitors back into the game.

The 19-year-old did exactly that, drawing the Red Devils level only five minutes after coming off the bench. It was an effort of the highest quality, too, as she exchanged passes on the edge of the box and then curled a superb strike beyond the despairing dive of Berger.

The goal seemed to wake Chelsea up, as we immediately went on the attack from the kick-off and very nearly restored our lead. The ball deflected into the path of Kerr on the left-hand side of the penalty area and she forced a brilliant save from Earps.

The United defence didn’t heed that warning, as we were back in front courtesy of the most direct goal one can imagine. Berger launched a clearance that the two centre-backs simply did not deal with, allowing it to bounce through to Kirby who had snuck in behind and, in the form she has been in, simply was not missing. The finish, clipped the other side of Earps as the keeper slid out to save, was of the highest order.

Considering how open the game had been for the opening hour or so, it came as little surprise to see Hayes look to shore things up. Ingle came on for Harder and immediately dropped in alongside Leupolz in midfield, while Bethany England added fresh legs to the attack in place of Kerr. Reiten wasn’t far behind them, as she replaced Ji.

Having largely gone blow for blow throughout this contest, the Blues showed exactly why we’ve gone almost two years without suffering a WSL defeat, on our way to equalling Man City’s 31-match unbeaten run.

There was barely a sniff at goal for Man United, who gave as good as they got at times, but simply couldn’t live with the champions across the 90 minutes. The referee’s full-time whistle indicated an end to their run at the top of the standings, as we leapfrogged them on goal difference. There’s still plenty of football to be played this season, but on an afternoon when Arsenal also dropped points against Reading, it could be a hugely significant weekend.

The Blues are next in action on Wednesday, as we take on Manchester City in our rescheduled Continental League Cup quarter-final. Then we travel to Bristol City on Sunday for a chance to maintain our place atop the league table and to make WSL history with the longest unbeaten run.

Chelsea (4-2-3-1) Berger; Mjelde, Bright, Eriksson (c), Andersson; Ji (Reiten 77), Leupolz; Kirby, Harder (Ingle 70), Cuthbert; Kerr (England 70)Unused subs Telford, Blundell, J Fleming, Charles, SpenceScorers Harder 30, Kirby 64Booked Reiten 90+4

Man United (4-2-3-1) Earps; Batlle, A Turner (c), M Turner, Smith; Ladd, Groenen; Hanson (Sigsworth 77), Toone, Galton; Press (James 55)Unused subs Bentley, Harris, McManus, Zelem, Fuso, Heath, RossScorer James 61Booked Groenen

Referee Rebecca Welch