Alexander Isak's penalty put Newcastle ahead in the fifth round tie at St James' Park.

Former Newcastle winger Yankuba Minteh equalised before the break, setting the stage for an explosive second half.

Newcastle forward Anthony Gordon was sent off for violent conduct in the 83rd minute after shoving Brighton's Jan Paul van Hecke in the head.

Brighton were also reduced to 10 men late in the second half when Tariq Lamptey was dismissed for a second booking.

Fabian Hurzeler's side emerged victorious thanks to Welbeck's strike in the closing stages of extra-time.

Brighton have never lifted the FA Cup and last reached the final in 1983 when they lost in a replay against Manchester United.

The Seagulls have won five successive matches since their 7-0 thrashing at Nottingham Forest.

They are through to the quarter-finals for the second time in three seasons after winning at St James' Park for the second time this season.

It was a bitter blow for Newcastle, who haven't won a domestic trophy since landing the 1955 FA Cup, while their last major trophy was the 1969 Inter-Cities Fairs Cup.

Unless Newcastle appeal against Gordon's three-match ban, they will be without one of their key players for the League Cup final against Premier League leaders Liverpool at Wembley on March 16.

- Brighton hit back -

Newcastle made a vibrant start as Harvey Barnes lofted a pin-point cross to the far post, where Isak blazed over from close-range after his initial effort was blocked by Adam Webster.

Isak tested Brighton keeper Bart Verbruggen with a long-range drive before Newcastle took the lead in the 22nd minute.

Minteh conceded a penalty with his rash challenge on Tino Livramento. Isak confidently lashed the spot-kick into the top corner.

It was Isak's 22nd goal in all competitions this season and the Sweden striker had the ball in the net again with a ferocious blast, only for an offside flag to curtail his celebrations.

Newcastle looked in complete command when Anthony Gordon cut inside for a curler that Verbruggen saved at full stretch.

But Brighton snatched an equaliser against the run of play in the 44th minute.

Joao Pedro's superb pass picked out Minteh inside the area and the Gambian's shot took a deflection as it flashed past Newcastle keeper Martin Dubravka.

It was a sweet moment for Minteh, who joined Brighton from Newcastle last year in a £30 million ($37 million) deal.

Gordon saw red with seven minutes left in normal time, the England star lashing out at Van Hecke as they challenged for the ball after play was stopped for offside against Isak.

Lamptey followed Gordon down the tunnel in stoppage-time after the Brighton defender's rash foul on Jacob Murphy.

Fabian Schar thought he had volleyed Newcastle's winner in stoppage-time, but the defender was ruled offside after a VAR check.

Brighton came on strong in extra time. Dubravka made a fine stop to keep out Diego Gomez's rocket from the edge of the area.

Newcastle had wilted and Welbeck won it for the Seagulls in the 114th minute, racing onto Solly March's defence-splitting pass and clipping his shot over Dubravka.