The Championship playoff final will take place on Sunday, May 26.
The play-off final is at Wembley Stadium on May 28.
The 34-year-old's crucial cameo role didn't go unnoticed by fans, who flooded social media to praise the Aussie legend.
Craig Dawson's header was the difference between the two sides over 120 minutes at The Hawthorns, leaving the score 2-2 on aggregate.More news: Michigan Legislature votes to ban abortion procedure
Albion had midfielder Chris Brunt sent off for a second yellow card in the 79th minute, forcing them to play the final 41 minutes with 10 men. Steer was the hero though, saving penalties from Mason Holgate and Ahmed Hegazi, as Tammy Abraham scored the winning penalty.
"There's obviously a lot of luck involved but wow", Steer told Sky Sports.
Jedinak came on with just seconds remaining in the match and - after Jed Steer put Villa in control with great saves from Mason Holgate and Ahmed Hegazi - slotted his side's second spot-kick easily.
After the game, Aston Villa manager Dean Smith said of Steer: "It's fantastic what can happen as Jed was at Charlton on loan earlier this year and now he's a hero for us".More news: Mortal Kombat Movie Set to be Filmed and Produced in South Australia
Marcelo Bielsa's Leeds hold a 1-0 first leg leads over Frank Lampard's Rams ahead of the second leg at Elland Road on Wednesday.
Aston Villa was in the final last season and lost to Fulham, which was relegated after just one season in the Premier League.
"All of us are very hungry and have good legs in us".
Norwich and Sheffield United were promoted automatically after finishing as the top two in the regular season.More news: Athletics trade Edwin Jackson to Blue Jays
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