Marcos Alonso netted an extra-time winner and Kepa saved an even later penalty as Chelsea fought back from conceding early on to advance to the FA Cup fifth round at the expense of a resilient Plymouth Argyle side.

The Pilgrims of League One took us all the way having gone ahead as early as the eighth minute through Macauley Gillesphey’s header. We hit the woodwork three times before Cesar Azpilicueta impressively drew us level as half-time approached, the skipper's delicate flick a fine way to open his account for the season.

We laid siege to Plymouth’s goal for large swathes of the second half, racking up 35 shots by full-time, but we could not find a way past Mike Cooper and his disciplined defence. One save from the young Plymouth stopper to deny Mason Mount was especially eye-catching.

The Blues, led by Arno Michels and Zsolt Low today with Thomas Tuchel self-isolating after testing positive for Covid-19, did muster a breakthrough at the end of the first half of extra-time. Sub Alonso was on the end of a slick move to make it two Spanish full-back scorers today.

Another Spaniard, Kepa, then reproduced his penalty-saving heroics to stop the tie going to a shoot-out. He guessed correctly to hold on to Ryan Hardie’s spot-kick with just a couple of minutes of the extra 30 remaining.

Credit must go to Plymouth who put in a tremendous showing and ran a very strong Chelsea side close, but it is our name that will be in the hat when tomorrow’s draw takes place. Before then, the Blues will fly to Abu Dhabi as attention turns to another cup competition, the Club World Cup.

The selection

As promised, Tuchel named a very strong starting XI to get his players back up to speed after a rare fortnight between games. In fact, Andreas Christensen for Thiago Silva was the only change from the team that so convincingly beat Tottenham in our last outing, with a back four again the formation of choice.

The Brazilian and Christian Pulisic were absent having been on international duty on the other side of the world this week, but will join up with the team before the flight to Abu Dhabi.

Kenedy was a substitute following his return to the group. Plymouth’s team contained former Chelsea Academy player Jordan Houghton.

Shock to start

The Pilgrims navigated some early choppy waters without too much alarm. The travelling support were briefly worried by a Jorginho daisycutter that skidded wide in front of them, but they were on their feet dancing with delight in the eighth minute when Gillesphey glanced in Houghton’s inviting free-kick.

Stunned by the goal, Chelsea set about restoring parity instantly, and within 90 seconds Mateo Kovacic was unlucky to see his powerful strike cannon back off the crossbar after Romelu Lukaku had teed him up.

The next big chance fell Plymouth’s way as they showed no signs of settling for one. Only a vital block from Malang Sarr stopped Panutche Camara’s goalbound strike testing Kepa.

Searching for parity

By the midway point of the half we had begun to settle down and assert our authority. A couple of vicious Hakim Ziyech corners caused the Pilgrims problems, and the same man tried his luck from the edge of the box, with a deflection making the save easier for Cooper.

On the half-hour we hit the woodwork again. Ziyech was the supplier in trademark style and his cross reached Hudson-Odoi, who couldn’t quite get under his close-range header enough. Azpi was the next to try his luck, stinging Cooper’s palms with a low drive.

When Kovacic rattled the left-hand post from inside the D on 36 minutes, you started to wonder if this wasn’t going to be our day.

Skipper to the rescue

Those fears were allayed five minutes before the break! It was another neat move down our right that prised Plymouth open, Jorginho slipping in Mason Mount. His low centre found the overlapping Azpilicueta, whose backflicked first-time finish was befitting of a Zola or a Hazard!

We nearly grabbed a second before the break, a tiny deflection taking Jorginho’s shot just wide, and from the resulting corner we couldn’t force the loose ball in. 1-1 and all to play for on a glorious winter’s afternoon in SW6.

Alonso emerged for the second half, replacing Christensen. Sarr shifted infield.

Chance after chance

As we upped the ante and pinned the Pilgrims back, Lukaku was centimetres away from turning in Ziyech’s low cross. Alonso was the next to test Cooper not long after some penalty-box pinball, and Azpilicueta had the ball in the net with another improvised effort, only to see the offside flag raised.

The hour mark ticked by as Plymouth dug in with everything they had. Kai Havertz for Hudson-Odoi was our second change, and the sub was soon in the thick of things. Kepa saved a Dan Scarr header and immediately released Havertz with a long kick. The German’s attempted pass square to Ziyech, who would have had a tap-in, was heroically intercepted by Joe Edwards.

Opening up but no decider

We kept knocking on Plymouth’s door. Ziyech’s clever pass inside found Azpilicueta who was denied by the feet of Cooper, and Sarr blazed over from the subsequent corner.

We were so nearly punished for our profligacy with 20 minutes left. Sub Hardie latched on to a through pass that split our defence open, but Kepa was out quickly to narrow the angle and make a vital save.

Down the other end, Cooper produced an even better stop from Mount’s rising left-footer following good Lukaku hold-up play. The tie remained on a knife edge as we entered the final 15 minutes. Timo Werner came on for Kovacic in an attacking move to try and avoid extra-time. Mount dropped into midfield.

A series of offside decisions and some drastic last-ditch defending continued to frustrate us, with the Pilgrims counting down the seconds until extra-time. As our corner tally approached 20, the shot count ticked past 30, but still we had just the one goal to show for our attacking efforts.

In the 90th minute, Lukaku slipped in Werner with space to run in to, but James Wilson got across to execute a sliding challenge before he could reach it, epitomising Plymouth’s defensive fortitude. Stoppage time passed without incident, so an additional half-hour it was.

Extra-time breakthrough

Attack versus defence remained the order of the day, but it felt like we had lost a little of our cutting edge compared to earlier in the tie. That was until Alonso struck gold in the first minute of added time!

It was a slick move. Werner and Havertz combined to release the latter, and his intelligent cutback found the bombarding Alonso who finished confidently on his right foot first time.

Attacking their travelling support for the second half of extra-time, Plymouth piled on the pressure when play restarted. Kepa did well to punch a corner away from under his own bar, and he then saved sub Ryan Broom’s fierce strike from range, with Sarr in the right place to block the follow-up effort.

However, the Frenchman was at fault for the Plymouth penalty that added an extra layer of drama to an engrossing Cup tie. His pass was intercepted by Hardie who ran clear and then received a nudge from Sarr, prompting the referee to point to the spot. But just as against Villarreal, Aston Villa and Southampton, Kepa displayed his mastery at stopping penalties, diving to his left and holding on to Hardie’s shot.

The Blues had made heavy weather of it, but battled over the line to book our place in the next round of the FA Cup, while Plymouth will return to Devon with plenty of plaudits.

Chelsea (4-2-3-1): Kepa; Azpilicueta (c) (Chalobah 112), Christensen (Alonso h/t), Rudiger, Sarr; Jorginho, Kovacic; Ziyech, Mount (Saul 97), Hudson-Odoi (Havertz 64); LukakuUnused subs Bettinelli, Sharman-Lowe, Kenedy, BarkleyScorers Azpilicueta 41, Alonso 105+1Booked Jorginho 19, Havertz 119

Plymouth (3-5-2): Cooper; Edwards (c), Wilson, Scarr, Gillesphey, Grant (Law 95); Camara (Broom 94), Houghton, Mayor (Randall 77); Garrick (Hardie 68), Jephcott (Ennis 58)Unused subs Burton, Bolton, Lewis, CraskeScorer Gillesphey 8Booked Cooper 102

Referee Simon HooperCrowd 39,959