A downpour less than an hour before start time took away any home track advantage for Wolves – and it took them a while to get dialled into their own circuit.
Peterborough won the opening three races and opened up an early six-point lead.
But Wolves finally began to show what they were made of in Heat Four when returning skipper Rory Schlein produced one of the rides of the season.
After missing the start, the Aussie bided his time before shooting past both of his opponents on the final lap to raise the roof on the Monmore terraces as the hosts claimed their first race win of the night.
Three straight 4-2s followed with Ryan Douglas rounding his rivals on the opening bends of the fifth before Nick Morris worked his way underneath Hans Andersen to earn third.
Wolves let a 5-1 slip in Heat Six and while Sam Masters went on to comfortably take the chequered flag, Luke Becker had to eventually work hard for third after falling to the back late on in the opening lap.
The scores tied after Heat Seven when Schlein made it two out of two and Broc Nicol fended off a wounded Michael Palm Toft, who crashed out of his opener, before Becker recorded his first victory in Heat Eight.
Peterborough regained control though and restored a two-point lead through Andersen and Pedersen in the ninth before Harris won Heats 10 and 11.
The Panthers then regained that six-point advantage in Heat 12 when Andersen picked up another victory while Scott Nicholls pulled off a smart cutback under Nick Morris mid-race off bend two.
Wolves responded with a first maximum of their own in Heat 13 through Schlein and Masters – and looked set for another in Heat 14.
But Andersen decided to stay down after sliding off to force a re-run and the Wolves had to settle for a 4-2 to level the scores with one to go.
There was drama in the original staging of Heat 15 when Schlein broke the starting tapes, and while replacement Nicol was able to split the Panthers pairing of Harris and Nicholls, Masters was unable to make an impact as the regular league leaders edged the victory.
The second leg takes place at the East of England Arena next Monday (October 4, 7.30).
WOLVERHAMPTON 44: Rory Schlein 10+1, Broc Nicol 8, Sam Masters 7+2, Ryan Douglas 7+1, Luke Becker 6, Nick Morris 6, Leon Flint 0.
PETERBOROUGH 46: Chris Harris 17, Scott Nicholls 12+2, Hans Andersen 11+2, Bjarne Pedersen 5, Jordan Palin 1, Michael Palm Toft 0, Ulrich Ostergaard R/R.