After a goalless first half, Wrack, who had not scored since January bagged two in the space of 16 minutes to stun the league leaders.
West Brom, like Walsall, took a while to establish themselves at Millmoor, but eventually took the lead shortly before half time when Shaun Barker inadvertently put the ball into his home net.
Rob Hulse made sure of the points after the interval with a goal on 49 minutes and another just after the hour mark to send Gary Megson's side top of the tree.
Sunderland lost ground at the top following a solitary goal defeat against Norwich City at Carrow Road.
Damien Francis netted the only goal of the game on 33 minutes, while Mick McCarthy's side left themselves a mountain to climb after the break when John Oster was shown a red card for striking Adam Drury.
Elsewhere, Bradford's poor home form continued following a last-gasp 2-1 defeat to Nottingham Forest.
Michael Branch had The Bantams ahead after just five minutes with a side-footed goal over Darren Ward.
Former player Eoin Jess levelled matters late on, before Andy Reid snatched a winning goal from the jaws of defeat.
Burnley shared the points at home to Millwall after Ian Moore's close-range strike equalised Noel Whelan's goal on 53 minutes.
Coventry secured their first away win at Derby since 1979 following a 3-1 success at Pride Park.
On loan Stephen Warnock fired Gary McAllister's side ahead early on, only for Patrick Suffo to add a second before the break.
The 16-year-old Lee Holmes pulled one back after half time, however Suffo's second late on made sure of the points.
Gillingham survived a scare at the Priestfield to beat Crystal Palace 1-0.
It looked bleak for the home side shortly after half time when Chris Hope was sent off and The Eagles were awarded a penalty.
Dougie Freedman saw his spot kick saved by Jason Brown, only for David Perpetuini to win the match at the death.
Preston's unbeaten home run continued after a 1-1 home draw to Ipswich Town.
David Healy opened the scoring in the first half, only for Pablo Counago to earn the East Anglian side a share of the spoils with a second half penalty.
Crewe had looked set to claim all three points at The Britannia Stadium, thanks to Steve Jones's goal, however Chris Greenacre snatched a draw in the last minute.
Wimbledon remain rooted to the foot of the table after a 3-1 home defeat to Watford.
Goals from Paul Devlin and Danny Webber had The Hornets two up at the break, however Mikeke Leigertwood gave The Dons hope with a goal just after the interval.
Any hopes Wimbledon had of claiming a point were extinguished when Scott Fitzgerald made it 3-1 late on.
Click below for match summaries:
Bradford 1-2 Nott'm Forest
Burnley 1-1 Millwall
Derby 1-3 Coventry
Gillingham 1-0 Crystal Palace
Norwich 1-0 Sunderland
Preston 1-1 Ipswich
Rotherham 0-3 West Brom
Stoke 1-1 Crewe
Walsall 2-0 Wigan
Wimbledon 1-3 Watford
Click here for the latest table.
