Sheffield Wednesday will take a two-goal lead into the second leg of their Championship play-off semi-final with Brighton after winning at Hillsborough.
After Wednesday’s Fernando Forestieri had seen a goal ruled out for offside, Ross Wallace scored from 25 yards.
The visitors lost four players to injuries, including top scorer Tomer Hemed and winger Anthony Knockaert.
With Brighton down with 10 men, Kieran Lee slotted in a second to stretch the Owls’ lead before Monday’s second leg.
Centre-back Connor Goldson and midfielder Steve Sidwell also left the field prematurely as the Seagulls, who narrowly missed out on automatic promotion by drawing at Middlesbrough on the final day of the season, saw their 14-game unbeaten run come to an end.
Hemed had already headed against the post for Brighton during a frenetic start before the biggest talking point of the first half.
Forestieri, standing several yards offside when goalkeeper Keiren Westwood cleared upfield, fired in low past Brighton’s David Stockdale for what he thought was the opening goal.
The home side were convinced that Gary Hooper had flicked the ball onto Forestieri – who by then had got himself into an onside position – but their protests were waved away by referee Andre Marriner, who consulted with his officials before deciding to disallow the goal.
Wednesday, in particular head coach Carlos Carvalhal, were incensed by the decision, which was later proved to be correct by television replays.
Injury woe for Brighton
Wednesday had only lost twice in the league at Hillsborough all season and Brighton’s chances of a positive first-leg result in South Yorkshire were severely hampered by the loss of four key men to injuries.
Already without defender Lewis Dunk and Dale Stephens because of suspension, as well as injured veteran striker Bobby Zamora, manager Chris Hughton was forced into two first-half substitutions when Goldson and Hemed left the field within 30 seconds of each other.
Sidwell followed soon after the interval and Brighton were faced with the prospect of playing the final 30 minutes with 10 men when Knockaert had to be carried from the field on a stretcher.
Dunk will return from his ban for the second leg, which a depleted Brighton will enter needing to overturn a two-goal deficit to reach the play-off final at Wembley on 28 May.
Chris Waddle, ex-Sheffield Wednesday winger on BBC Radio 5 live
“This game’s not finished. Sheffield Wednesday could have put it to bed. Give Brighton credit, they’ve had a horrendous night with injuries and everything’s been against them.
“I thought Sheffield Wednesday were excellent in spells tonight. I just hope they don’t regret killing this game by three or four.”
Sheffield Wednesday head coach Carlos Carvalhal: “I think we did one of our best performances of the season and if you exclude a moment when Brighton had a chance early on, I think we played very well.
“We are happy about the game and the score but we know we have won absolutely nothing – we have the advantage but we must understand that we can’t play thinking we are winning 2-0.
“The game will start at 0-0 and we will do our best to get a good result at Brighton.”
Brighton manager Chris Hughton: “The injuries were all substantial enough to go off and not one of them wanted to go off. At the moment I wouldn’t be too optimistic about all four of them.
“I’ve never been involved in a game like that. We’ve gone through a decent period with injuries after a really tough period in the first half of the season, and whether it’s the consistent games and the tempo we’ve had to play at in the last few weeks, I don’t know.
“We have to be realistic enough to know it’s going to be a tough task, but it is something that can be achieved.”