IT could come down to the influence two 35-year-old strikers this Sunday.
Millwall skipper Steve Morison and Brighton's Glenn Murray – born a month apart in 1983 with the latter the younger man – have both been big influences in their sides' progression to the last eight.
Morison, seconds after coming on, won the free-kick that led to Murray Wallace's sensational last-minute winner against Everton in the fourth round.
Former Crystal Palace forward Murray hit two extra-time goals to clinch a 3-1 win at West Brom in the last round.
Murray scored his 13th of the season in a 2-1 win over bitter rivals Palace at Selhurst Park last in the Premier League weekend. He was initially named as a substitute before Florin Andone got injured before the game.
Morison expects Murray to be a "handful" if he features this weekend.
"I've played against him. He's doing fantastically well, still scoring goals at the top level," Morison said. "You listen to commentators and they always like to comment on people's age, saying their legs have gone and all that kind of stuff. He shuts up the critics all the time.
"The best thing about the weekend was the fact that he wasn't even supposed to be playing before Andone got injured in the warm-up. He played and it shows that when you get to a certain age you're always mentally ready.
"I'm sure he'll be a handful for our back four on Sunday."
If Millwall win, then Morison will be in a position to lead his side out at Wembley for a second time in three seasons after 2017's League One play-off final against Bradford.
But he isn't allowing himself to look past Sunday.
"It would be massive, it would be brilliant for the football club," he said. "You know what it's like, you can't look further than this game because you could fall flat on your face talking about that.
"If we get through then I'd love to be involved."
Ben Thompson, Ben Marshall and Fred Onyedinma are cup-tied for Millwall, and cup hero Wallace is injured. Lee Gregory is a slight doubt after going off against Birmingham on Wednesday.
Like Millwall, Brighton boss Chris Hughton's priority is avoiding relegation. The Seagulls are five points above the bottom three but have a game in hand on the five sides below them.
"Staying in this division is still the most important thing to me," Hughton said. "I know what staying in the cup means to the supporters and hence that's why we've given everything we can in the cup and we will do on Sunday.
"Making sure we're in this division next season in my thinking is the most important thing. Any progress we can make in the cup is a brilliant bonus for us."
Hughton has fielded weakened sides in the competition so far this season, but with an international break following the game he could be tempted to show a stronger hand. He will be without Florin Andone, Pascal Gross and Yves Bissouma.
Possible Millwall team
Archer; Romeo, Hutchinson, Cooper, Meredith; Wallace, Tunnicliffe, Williams, Ferguson; Leonard; Gregory.
Millwall 5/2 Draw 11/5 Brighton 11/10
2014-15 Championship: Millwall 0-0 Brighton
Image: Millwall FC