Martin Bavidge's late winner meant Peterhead left Firhill with a one-goal lead after the first leg of their Division One play-off final.
Martin Bavidge (right) scored the winner for Peterhead
Peterhead's Allan Youngson had an effort cleared off the line before Billy Gibson headed Partick Thistle ahead following a Mark Roberts cross.
Goalkeeper Kenny Arthur denied Bobby Linn but then looked at fault as Graeme Sharp forced the ball home.
And Bavidge fired in the winner only seconds after coming on as substitute.
Peterhead had won three and drawn one of the meetings between the sides during the Division Two campaign.
But it was no surprise that it was a tight affair between teams who finished the season level on points.
Peterhead had been forced to bring in Youngson in place of midfielder Keith Gibson, who had been up all night attending the birth of a new baby.
Thistle had also made one change, fit-again Scott Boyd replacing the injured Darren Brady in midfield.
And it was the player on loan from Livingston who cleared off the line from Youngson's attempt to finish from a Jamie Buchan pass.
Billy Gibson opened the scoring for Thistle
Thistle midfielder Adam Strachan fired over after being set up by Stephen McConalogue 12 yards from goal.
And McConalogue forced a fine save from Stranraer goalkeeper Paul Mathers with a shot on the turn.
Linn curled an effort just wide as Peterhead concentrated on hitting on the counter-attack.
But, once Gibson had put Thistle ahead, Peterhead boss Iain Stewart's tactical changes saw his side pose a greater attacking threat after the break.
Arthur denied Linn after the striker was put through one-on-one by a fine ball from former Thistle midfielder Buchan.
But Arthur was left claiming in vain for a foul when Sharp challenged him when racing on to a Chris Hegarty through ball.
It was Mathers' turn to pull off a superb save to stop a McConologue shot.
And Linn fired the ball wide at the other end after again beating the offside trap.
Strachan shot just wide after a superb run as play raged from end to end.
And Bavidge side-footed the ball home to give Peterhead the advantage ahead of Sunday's second leg.
Partick: Arthur, Murray, Smyth, Hodge, McCulloch, James Gibson, Boyd, Billy Gibson, Strachan, McConalogue (Ritchie 80), Roberts.
Subs Not Used: Colin Stewart, Snowdon, Nicholas, McGoldrick.
Goal: Billy Gibson 34.
Peterhead: Mathers, Calvin Shand, Tully, Perry, Cameron, Sharp, Buchan, Youngson (Hegarty 48), Linn (Bavidge 81), Wood, Nicol.
Subs Not Used: McCafferty, Michie, Stephen.
Booked: Calvin Shand.
Goals: Sharp 59, Bavidge 85.
Ref: S Dougal