Killian Phillips' double ensured St Mirren survived an Ayr United fightback to secure qualification for the Premier Sports Cup last 16 as Group D winners.

The Championship visitors, who started the day two points clear at the top, also progress as one of the three best runners-up, comfortably ahead of Dunfermline Athletic on goal difference.

St Mirren went into the game knowing they only needed to draw with a penalty shoot-out bonus point to reach the last 16, but the Premiership side were obviously hell bent on progressing as group winners.

The breakthrough came with the hosts' first effort on goal after 16 minutes, Phillips' low, first-time drive from a Roland Idowu cross evading David Mitchell too easily for the goalkeeper's liking.

Unmarked, Phillips added his second - and fourth in two games - seven minutes before the break, side-footing home another low cross from his fellow midfielder.

Ayr, who knew they would qualify as runners-up unless they lost by nine or more goals after winning their opening three games, lacked a cutting edge and could not muster an attempt on target in a lacklustre first half.

St Mirren should have extended their lead when Mikael Mandron fired wastefully over the crossbar.

However, visiting manager Scott Brown's second-half changes invigorated Ayr and winger Dom Thomas curled a drive just wide before his corner was headed home by midfielder Kevin Holt.

Two more Thomas corners found fellow substitute George Oakley and Holt, but both headers were comfortably held by debutant goalkeeper Shamal George.

Although Mark O'Hara missed a late chance to restore the lead when the midfielder fired wide when clean through on goal, two goals were enough for St Mirren.

The Buddies' reward is a home tie against top-flight rivals Heart of Midlothian, while Ayr are away to fellow Championship side Partick Thistle.

St Mirren manager Stephen Robinson: "The way we played in the first half, I thought we were outstanding. We got a little bit casual in the second half and didn't do the simple things well.

"We lose a goal from a set-play and the momentum swings and puts us on the back foot, but we showed the character and quality and we should have gone and finished the game off with three or four more goals."

Ayr United manager Scott Brown: "It was a game of two halves. They dictated the first half and we were a little bit sloppy in our shape, but in the second half we looked like the team on the front foot, we had more chances and more possession of the ball.

"In the first half, I probably did get it wrong. Gave them a little too much respect and I think, if we went after them a little bit more and put them under pressure, and had the personnel that we finished the game with, we would have caused them a lot more problems.

"That's us competing against a top-six team and we didn't look out of our depth at all."

Did you take in St Mirren's win or were you following from elsewhere?

Have your say on the match