Peterhead will go into Saturday’s League One play-off semi-final second leg 2-1 down following a controversial stoppage-time penalty winner for Spartans at Ainslie Park.
After a lively beginning to proceedings, it was the visitors who stormed ahead after only eight minutes, Hamish Ritchie catching the Spartans defence napping with a long ball over the top which fell nicely to the unmarked Conor O’Keefe. He had time to steady himself before sending a measured lob over the stranded Blair Carswell and into the empty net.
The Edinburgh side almost equalised in the 16th minute, top-scorer Henderson charging into the penalty area from the left-hand side before laying the ball on a plate for strike partner Marc McNulty, whose shot was blocked by Ryan Strachan.
Spartans drew level from the resultant corner, though, the Peterhead defence failing to deal with Cammy Russell’s cross, leaving Paul Watson free to drive the ball past Stuart McKenzie from eight yards out.
Kieran Shanks twice tested Carswell as the Blue Toon battled to regain the advantage before half-time and the Spartans keeper was again called into action shortly after the break, diving to block a blistering 20-yard shot from Flynn Duffy.
Peterhead looked by far the hungrier side in the second half, their cause aided by the introduction of talismanic frontman Rory McAllister.
But Spartans almost took the lead with 17 minutes remaining when a 25-yard free-kick from James Craigen almost deceived McKenzie, who managed to touch the ball away for a corner.
With a draw looking the likely outcome, Henderson’s 91st-minute close-range shot hit the crossbar and, in the ensuing scramble, a penalty kick was awarded following a foul by Danny Strachan.
The Spartans striker converted the award with panache to seal the first leg victory.
It left promotion-chasing League Two runners-up Peterhead with a deficit to overturn if they are to keep their promotion dream alive by despatching the side who finished a place below them at Balmoor this weekend.
Co-manager Jordon Brown said: “It feels sore but we have to remember it’s just half-time in the tie.
“I think for the best part of the 90 minutes tonight we did everything we needed to do to win the game, so to get sucker-punched like that right at the end has really hurt us.
“It’s frustrating, but we just need to take it on the chin, regroup and go again on Saturday.”
In the other League One play-offs semi-final, League Two’s fourth-placed side Dumbarton made home advantage count to take a 2-1 lead over third-tier ninth-placed finishers Stirling Albion going into their second leg.