Olivier Giroud links Arsenal and Chelsea and a man with a remarkable record in the FA Cup helped ensure his current club will face his former employers in August’s final. And yet, while victory reflected his increasingly talismanic status, was a tactical triumph for Frank Lampard and included an own goal by Harry Maguire, it came gift-wrapped by David de Gea who, as much as anyone, ended Manchester United’s 19-game unbeaten run. This amounted to another traumatic outing for him. Ole Gunnar Solskjaer has a tendency to parrot United’s party line that the Spaniard is the best goalkeeper in the world, but he isn’t. He isn’t even close. He has made far too many errors in the last two years and if it is a moot point if Giroud’s goal classed as a De Gea mistake, there is no doubt Mason Mount’s strike did. So it is Lampard, rather than Solskjaer, who will take on Mikel Arteta in a final that will provide a first major piece of managerial silverware in England and vindicate the appointment of a rookie. His debut year could bring glory and, as in 2002 and 2017, the FA Cup showpiece will be an all-London affair between capital rivals. Giroud has won the competition three times with Arsenal and once with Chelsea. He has experienced much at Wembley but a goal in the 56th minute of the first half felt new. It came because a head injury to Eric Bailly delayed proceedings and, on a day when much went wrong for United, this felt the most painful. Solskjaer’s gameplan had brought him three wins against Chelsea this season but Lampard was rewarded for a rethink. He adopted a back three and it proved a masterstroke. Chelsea were outstanding, stronger and fresher. In United’s defence, they had two days’ less rest so rotation may have been required. Solskjaer demoted Anthony Martial, Mason Greenwood and Paul Pogba to the bench and changed shape. He brought in Bailly to revive an old policy of facing Chelsea with three centre-backs. It had worked for him in winter, but not in summer. The luckless Bailly was stretchered off in a neck brace after two clashes of heads, the second with team-mate Maguire. It was significant his replacement was Martial with Solskjaer changing system after his side’s slow start. Lampard’s like-for-like tactics may have been designed to compensate for the absence of the injured N’Golo Kante. They worked. His back three were resolute and Mateo Kovacic was terrific in an energetic midfield. Chelsea’s wing-backs had a licence to roam forward and they mustered the first efforts. Reece James produced a ferocious long-range effort that De Gea parried while Marcos Alonso headed Cesar Azpilicueta’s centre over the bar. The captain resumed the right centre-back role he often had under Antonio Conte and his crossing was a factor when Chelsea broke through. Found by James, he delivered the low ball Giroud met with a deft flick. De Gea got a hand to it and probably should have saved it, but the ball trickled over the line. Lampard may have been too slow to appreciate Giroud’s attributes but, since becoming a regular in February, he has been terrific. If the goalkeeper was possibly culpable for the first, he was definitely culpable for the second. Brandon Williams was at fault, too, with a cross-field pass that Mount intercepted. The Chelsea midfielder shot from 25 yards but it was far from his sweetest strike. De Gea merely pushed it into the net. While the world’s best-paid goalkeeper blundered, the most expensive watched on from the bench. Kepa Arrizabalaga was omitted for Willy Caballero. The veteran was not required for half an hour as United were muted, until he tipped Bruno Fernandes’ free kick over the bar. Marcus Rashford’s speed on the break offered a first chance in open play, when he shot across the face, and Solskjaer sent for the cavalry. Still, however, a team who had been potent of late struggled to create. They were subdued and substandard, snuffed out by Chelsea’s system and solidity. United brought on Greenwood and Pogba and finally scored, when one substitute, Martial, was fouled by another, Callum Hudson-Odoi, and the nerveless Fernandes converted the penalty. But United had opened up and Chelsea’s chances brought their third goal when Maguire accidentally turned in Alonso’s cross. Before then, Mount fired over and De Gea clawed away another Giroud shot and James’ header. Yet his impact was of the wrong kind. It is Chelsea who will return to Wembley.