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Steven Lawless (right) gave Thistle the lead from the penalty spot

Partick Thistle reached the League Cup quarter-finals for the first time since 2014 as they knocked out St Johnstone at McDiarmid Park.

Thistle took the lead when Kevin Nisbet was brought down by Joe Shaughnessy and Steven Lawless scored the penalty.

Ryan Edwards then thumped in an outstanding strike from 20 yards.

Chris Erskine rounded off the win after jinking his way into the box and picking his spot beyond goalkeeper Alan Mannus.

Saints were left to rue missed chances with Steven Anderson heading wide and Graham Cummins missing when one-on-one with the goalkeeper.

Nisbet was handed his second start for Thistle after Kris Doolan picked up a hamstring injury and the 20-year-old showed his youthful innocence early in the first half when he stayed on his feet after having his ankle clipped as he turned inside Anderson.

The striker had a shot blocked but had been knocked off his stride by the challenge and referee Euan Anderson played on.

Nisbet got the only shot on target of the first half after robbing Shaughnessy and showing good feet before his near-post effort was blocked by Mannus.

The visitors were again without the injured Blair Spittal and they lost Danny Devine on the half-hour mark after he failed to run off an early knock.

After an uneventful first half, it was no surprise that the breakthrough came from a set-piece - but the penalty award shocked the hosts as Anderson claimed he got the ball as he and Nisbet chased Erskine's forward pass.

Partick Thistle's Steven Lawless (second left) celebrates his goal

The striker was going away from goal just inside the box and Lawless took full advantage of the unexpected chance by sending Mannus the wrong way.

Anderson quickly had a header cleared off the line by Erskine before Nisbet twice curled shots wide from just outside the box.

Saints skipper Anderson's nightmare continued when he somehow sent a free header wide from six yards following Wotherspoon's cross.

And Edwards lit up the game when he curled into the top corner after a neat exchange of passes just outside the Saints box.

The hosts had a chance to get back into it when Steven MacLean threaded Cummins through but the substitute lacked composure and sliced wide from 18 yards.

Saints continued to press but it was evident it was not to be their night when Shaughnessy failed to beat Tomas Cerny from six yards - and that was confirmed when the referee waved away penalty appeals as Cummins went down under the aerial challenge of Niall Keown.

And Erskine soon raced away to finish in style after an excellent flick-on by Nisbet.

Post-match reaction

St Johnstone manager Tommy Wright: "The score probably doesn't reflect the game but we're out of the cup because we haven't done well enough.

"In terms of chances we had enough good opportunities. We were trying to walk the ball into the net. It was a rusty performance in front of goal. They were ruthless.

"There's positives in the number of chances we created in the second half. The negative side is we're out of the cup and we could have defended the first and third goals better."

Partick Thistle manager Alan Archibald: "It's a really tough place to come and the first goal is often the winner.

"I'm delighted for Ryan Edwards. He didn't have the best of pre-seasons but he certainly made a difference to the team tonight.

"Hopefully we can kick on in the league now. We've got a tough one next with Celtic but thankfully we're in the next round."