Andre Ayew's superbly-worked goal earned Swansea City a 1-0 victory over Brentford in the Championship playoff semifinal first leg at their Liberty Stadium on Sunday.
Ayew had seen his poorly-struck penalty saved just past the hour mark before Brentford had Rico Henry sent off.
Swansea then swarmed all over Brentford seeking a crucial lead to take into the second leg next week and got it when Ayew fired into the top corner after an intricate build-up.
Brentford, who have not been in the top flight since 1947, missed out on automatic promotion on Wednesday when they lost at home to Barnsley, meaning West Bromwich Albion finished as runners-up behind Leeds United.
Swansea crept into the playoffs after a remarkable final round of fixtures in which they beat Reading 4-1 and jumped above Nottingham Forest, who lost 4-1, on goal difference.
Promotion to the Premier league is worth an estimated 170 million pounds ($217.41 million). Cardiff City take on Fulham in the other semi-final.
Brentford had the better of the first half with Ollie Watkins and Said Benrahma both missing chances to put them in control, although Ayew and Rhian Brewster came close for the Swans just before the interval.
The visitors continued to threaten after the break with Mathias Jensen dragging a great chance wide.
Swansea were then awarded a penalty when Brewster was tripped by Brentford captain Pontus Jansson but Ayew's effort was kept out by David Raya.
It looked like being a key moment but that was still to come as Henry's high-speed sliding tackle on Connor Roberts was deemed dangerous and worthy of a straight red card.
Ayew, who re-joined Swansea in 2018 having left to join West Ham United, made amends for his miss, volleying home after a sweet move which he started. Ayew played the ball in to Conor Gallagher whose dink was cushioned to Ayew by Jay Fulton and the Ghana international smashed the ball home.
"Andre brushed off the disappointment of the penalty and didn't let that affect him, but that's what he does, step up in the big moments," Swansea coach Steve Cooper said.
Brentford will now have to bounce back after three successive defeats.