St Mirren 1 Celtic 0: Billy Mehmet's second-half penalty gave St Mirren a sensational Scottish Cup quarter-final victory over Celtic — a week after the Buddies lost 7-0 at Parkhead in the Scottish Premier League.

There were 55 minutes played when Celtic captain Stephen McManus felled Craig Dargo inside the box and English striker Mehmet sent Artur Boruc the wrong way from the spot.

Celtic threw everything forward, especially in the latter stages, in a bid to keep their hopes of a domestic treble alive, but the Buddies defended resolutely to book their semi-final spot.

The final whistle brought elation to the home fans among the crowd of 5,925 and also to goalkeeper Chris Smith who made up for his Parkhead nightmare with a fine save at the end from a Jan Vennegoor of Hesselink header to prevent a replay.

The home side started as though they had wiped clean the memory of their drubbing in Glasgow. In the second minute, following the home side’s first corner of the game, Boruc was forced to make a good save from Garry Brady’s angled volley.

The first scare for St Mirren came moments later when goalkeeper Smith looked hesitant in dealing with Celtic right-back Andreas Hinkel’s long ball to the back post, but Vennegoor of Hesselink was too slow to get a proper connection.

In the 14th minute, as both sides tried to come to terms with the swirling wind, Scott McDonald had the ball in the net from Shunsuke Nakamura’s cross but was ruled offside.

Possession changed hands with startling regularity as St Mirren’s tactics of harrying the Parkhead side added to the usual freneticism.

Strikers Mehmet and Craig Dargo tried to keep the Celtic rearguard busy but it was as the first line of defence rather than in a more positive way.

Celtic became stronger as the half continued but they struggled to penetrate, typified when midfielder Aiden McGeady’s right-footed shot from 25 yards saw Smith save with more ease than he had displayed in dealing with a couple of previous back passes.

Nakamura curled in a couple of dangerous free-kicks from the left which came to nothing but by the time the interval arrived the momentum was clearly with the Hoops.

Five minutes after the restart McGeady got the break of the ball from former Celtic defender Mo Camara but fired wide of the target from 25 yards. Moments later, from a Nakamura corner, Celtic’s stand-in left-back Darren O’Dea rose high inside a packed six-yard box to head over.

But in the 55th minute Saints found themselves dramatically ahead after they were awarded a penalty when McManus chopped down Dargo as the former Kilmarnock striker burst into the Celtic box.

To the annoyance of the home support, mindful that Jack Ross was red-carded for a similar incident involving McDonald last week at Parkhead, McManus was only booked by referee Charlie Richmond.

But they were soon cheered when Mehmet sent Boruc the wrong way from the spot. The goal changed the dynamic of the game and as Celtic stepped up the pace, Nakamura had three more flighted free-kicks repelled by the Buddies defence.

The final whistle looked a long way off as Gus MacPherson’s men were slowly pressed further back towards their own box.

Yet the Parkhead side were caught on the break with 10 minutes remaining and Boruc was forced to make another good save, this time from Andy Dorman.

Smith made a decent block from McDonald in the final few minutes and then an even better one from Vennegoor of Hesselink’s point-blank header from a Nakamura cross.

But in the end, there was too much determination in the home side to let this chance of history slip.