Super-sub Scott Fraser was the hero for Dundee United with a superb left-footed finish five minutes from time.
The goal was fit to win any game, the impressive Blair Spittal deceived the Jags defence with a clever reverse pass into Fraser’s path and he side-footed the ball into the far corner.
The goal aside, it was a match devoid of any real clear cut chances.
United forced a couple of saves out of Partick keeper Tomas Cerny in the first half through John Rankin and Simon Murray while Murray came within inches of connecting with a Rankin drive across the face of goal midway through the second half.
Alan Archibald’s men struggled to test the United backline.
Substitute David Amoo missed their best chance when he was played in on goal but he never realised he was onside and clashed with Arabs keeper Kawashima and the chance was gone.
It wasn’t pretty but the Mixu Paatelainen rebuilding job continues and the Arabs fans can look forward to the quarter-final draw on Monday.