MIXU Paatelainen saw his Dundee United players rewarded for their persistence as they reached the quarter-finals of the William Hill Scottish Cup.

A typically tough cup tie looked to be heading for a replay at Firhill on Tuesday night, until United substitute Scott Fraser struck five minutes from time, firing home left-footed after collecting a pass from Blair Spittal.

The Tannadice manager said: "We've got to be delighted with the result. It's a very good feeling to be through. That was the aim and we got there in the end. It wasn't the best performance-wise but we fought for it and that's what you have to do."

Paatelainen said of the goal: "It was a fantastic finish. Fraser is a good finisher with great technical ability. It was great to see the ball hit the back of the net.

"We want to build on this and try to win every game. That's us with two wins in a row and we just have to keep going."

The teams were due to meet last weekend on league business, but Firhill was ruled unplayable.

Thistle arrived on Tayside buoyed by Tuesday night's 1-0 SPFL Premiership win over Motherwell which came courtesy of Steven Lawless's last-minute goal. They started well and in the ninth minute Sean Welsh's 22-yard shot was spilled by home goalkeeper Eiji Kawashima but the United defence hooked the ball to safety at the expense of a corner.

United were finding it hard to get going but after 18 minutes midfielder John Rankin forced his way into the box. However, his shot was deflected wide by Frederic Frans.

The visitors looked the likelier side to make the breakthrough and before the half-hour, Callum Booth aimed a cross from the left at for Lawless, but Kawashima came off his line to smother it.

At the other end, the hosts finally put together a flowing moved when Guy Demel fed Billy Mckay. He in turn released Simon Murray, who tried to angle his shot across the body of Tomas Cerny, but the visiting goalkeeper held it well.

The second half started with Demel linking with Blair Spittal. Paul Paton then shot high over the bar from 25 yards.

Thistle made a double substitution in the 64th minute in a bid to win the tie, with Mathias Pogba and Gary Fraser replacing Welsh and Kris Doolan.

United almost opened the scoring three minutes later. Rankin went on a surging run down the left before crossing low into the six-yard area where Murray was lurking but he just missed out.

In the 76th minute Fraser's goalbound shot was deflected wide by Welsh but he was not to be denied. He latched on to Spittal's pass and steadied himself before slotting a left-foot shot into Cerny's far post for the winner.

Partick manager Alan Archibald said: "It was a sore one with the late goal. I don't think anybody deserved to win the game, it looked like a draw all the way.

"There wasn't a lot of quality. Defensively we were good up until the goal. We lost the ball in a bad area and they scored with a bit of quality.

"We changed the shape to combat the way United play. They are very, very direct with their two boys up front. I thought we handled that but we didn't create enough.

"We had a wee spell in the second half before the substitutions but it filtered away. David Amoo had what looked like a half-chance. The goalie maybe came out and put him off. We had a few flashing across the box but we didn't really work the goalie enough."