This semi-final tie at Kingsmeadow was effectively over inside half an hour, as we netted four times to leave the Hammers wondering what had hit them.

Indeed, only three minutes were on the clock when Harder opened the scoring and it was a wonderful finish by the former Wolfsburg forward, who took a pass from Ji So-Yun in her stride and clipped the ball past Mackenzie Arnold.

The visitors were just about managing to keep up with Emma Hayes’s side, but a couple of mistakes from their Australian goalkeeper turned an already uphill struggle into a mountain to climb.

First, she allowed a speculative long-range effort from Sophie Ingle to squirm underneath her body, before presenting the ball to Harder inside the penalty area to make it 3-0 to the Blues.

Two minutes after the Dane’s second of the evening, we were four goals to the good, and this was the pick of the bunch. Ingle was involved again, playing in Fran Kirby down the right and her low cross was fired in at the near post by Bethany England.

The result was never in doubt, but the Blues put the seal on a wonderful display in the second half when Kirby got the goal her performance had merited, netting at the second attempt after her initial effort was saved.

That was followed late on by a lovely strike by Harder, who cut in from the left and whipped in a shot at the near post that meant she’d take home the match-ball for the first time in a Chelsea shirt, as well as moving her on to nine goals for her new club this season.

The Blues will now head to Watford’s Vicarage Road on Sunday 14 March for the 10th Continental League Cup final, when we’ll face Bristol City or Leicester City knowing we are potentially only 90 minutes away from retaining the trophy we won for the first time last season.

Before that, though, there is plenty of work to be done to maintain our lead at the top of the WSL standings, starting with a home game against Brighton on Sunday. Kick-off is at 2pm and you can see all the action live on the 5th Stand app (geo-restrictions may apply).

Despite only a three-day turnaround from our last game, Hayes largely kept faith with the same side that made light work of Tottenham Hotspur on Sunday, opting to make only two changes. Guro Reiten and Sam Kerr were the players to miss out, as Ingle and England were restored to the starting XI.

There was a change of shape, however, but only in front of the tried and tested back five of goalkeeper Ann-Katrin Berger, Maren Mjelde, Millie Bright, Magdalena Eriksson and Jonna Andersson. A midfield three of Melanie Leupolz, Ingle and Ji offered the perfect mix of grit and guile, while there was plenty of fluidity to our front three of Kirby, England and Harder.

That was on display as early as the third minute, when the latter drifted from her nominal position on the left-hand side over to the right, from where she scored the game’s opening goal. West Ham’s midfielders were far too passive in allowing Ji to run unchallenged from deep and when the South Korean has time to pick a pass, it usually means bad news for the opposition. The timing and weight of her through-ball to Harder was immaculate, allowing her to take the ball in her stride and clip a confident finish over the onrushing Arnold.

An early goal against another side who play in claret and blue, Aston Villa, set us up for a comfortable win this time last week, and it was quickly apparent that the Hammers’ five-player defence may ensure plenty of bodies at the back, but not necessarily in the right position.

Indeed, it was becoming increasingly apparent that there was too much space being left between the left-sided centre-half and the wing-back on that side, as Kirby found out to her delight. However, our No14 was dragged a little wider than she’d have wanted, so she hammered a low cross which went straight across the goal-line. Somehow the Hammers emerged with possession and only a one-goal deficit.

That would not be the case for much longer, as Ingle netted from distance for the second round in succession in the Conti Cup. Unlike her Goal of the Season contender against Manchester City, however, this one owed much to the failings of West Ham’s Australian goalkeeper, who allowed a left-footed strike to squirm through her grasp and into the back of the net.

Arnold’s night was to go from bad to worse, as she committed another error to put one on a plate for Harder. The Hammers were looking to play their way out from the back, but when former Chelsea centre-back Gilly Flaherty went back to Arnold, she fluffed her clearance and presented the ball straight to Harder, who fired home.

Two minutes later, we were out of sight, and this time there was absolutely nothing West Ham could have done about the most clinical of counter-attacks. A peach of a pass from Ingle left Kirby with time and space down the right to pick out a team-mate, which she did to find the run of England to the near post. The Blues No9 simply does not miss from that range, as she emphatically finished off a wonderful move to make it 4-0. Only 27 minutes had been played; it was clearly going to be a long night for the visitors.

Despite there being more than two thirds of this contest to run, it was all over bar the shouting. For the remainder of the first half, West Ham went into damage-control mode, while the Blues were clearly content to preserve energy and retain possession. Professionalism was the order of the day here.

The second half, however, began with a bang, as Kirby and England both forced Arnold into action just after the interval. On both occasions the keeper showed why she’s the Hammers’ No1, as she pulled off a couple of fine saves.

West Ham began to show a bit of quality in the attacking third for the first time, briefly putting us under pressure, and Hayes made the most of her star-studded subs bench when she made a triple change just past the hour mark. Erin Cuthbert, Hannah Blundell and Jessie Fleming were the players to enter the fray, in place of Andersson, Leupolz and Ji.

Cuthbert almost made an inauspicious return to Chelsea action, as her misplaced pass allowed Leon to bear down on goal, only for Eriksson to time a last-ditch challenge to perfection. Pacheco was denied by Berger from West Ham’s next attack, as the visitors looked to grab a consolation.

Instead, the next goal came at the other end just a minute or so later, and it was Kirby who scored it. Mjelde was the creator, fizzing in a low cross that Super Fran attempted to loop over Arnold, and though the keeper got her hand to it, our leading scorer was on hand to turn home the rebound and make it 5-0.

That was Kirby’s last meaningful action, as she and Eriksson earned a well-deserved rest when they were replaced by Reiten and Drew Spence for the final stages of a comfortable victory for the Blues. There was still time for one final flourish, though, as Harder completed her maiden hat-trick for the club with a wonderful finish. Blundell’s pass allowed her to cut in from the left-hand side and fire a low shot past the despairing dive of Arnold, completing a wonderful performance from our No23.

We could have had another deep into stoppage time, had Reiten’s stunning free-kick been a few inches lower, as it rattled the crossbar and flew away to safety. Still, it had been some night for the Blues in our 20th outing of the season, of which we have now won 17. Six goals, none conceded and a place in a cup final – not a bad evening’s work.

Our next game takes place on Sunday, as we play the third of four home matches on the spin with a WSL fixture against Brighton. Kick-off is at 2pm and you can see all the action live on the 5th Stand app (geo-restrictions may apply).

Chelsea (4-3-3) Berger; Mjelde, Bright, Eriksson (c) (Spence 77), Andersson (Blundell 62); Leupolz (Cuthbert 62), Ingle, Ji (Fleming 62); Kirby (Reiten 77), England, HarderUnused subs Telford, Carter, KerrScorers Harder 4, 25, 86, Ingle 15, England 27, Kirby 70

West Ham (5-4-1) Arnold; Redisch, Fisk, Flaherty (c), Vetterlein, Pacheco (Barker 87); Joel, Longhurst, Van Egmond, Svitkova (Thomas 73); LeonUnused subs Brosnan, Cissoko, Dali, NorBooked Longhurst 90+2

Referee Stacey Pearson