A deflected first-half strike from Thomas Ince sealed a 1-0 win for Blackpool over Birmingham in the first leg of their Championship play-off semi-final on Friday.
Blackpool, who were relegated from England's top flight after the 2010-2011 season, will now take their slender advantage to St Andrews next Wednesday for the second leg.
On Thursday West Ham beat play-off opponents Cardiff 2-0 away in the Welsh capital to take a major stride towards securing a place in the play-off final at Wembley on May 19.
The clubs will meet for the second leg at West Ham's Upton Park on May 7.
Championship winners Reading and runners-up Southampton claimed the two automatic promotion places on offer and are assured of playing in the lucrative English top flight next season.
But the four clubs immediately below the Saints must battle it for the one remaining spot in the top flight via the playoffs, which culminate with the Wembley final.