Johnny Russell's first-half goal made the difference as Dundee United defeated second-placed Motherwell 1-0 at Fir Park.
The hosts had plenty of the game as they looked to go five points clear of third-placed Inverness but Dundee United created a string of chances on the break and could have won more easily.
Motherwell made the brighter start and Chris Humphrey shot wide, before Henrik Ojamaa played a dangerous ball into the area which no one could get on the end of.
But Dundee United began to get into the game after around 10 minutes, with Johnny Russell and Stuart Armstrong looking dangerous on the counter-attack.
And the visitors took the lead in the 17th minute with a fine goal, Gary Mackay-Steven advancing 50 yards before playing in Russell, who beat the offside trap and slid the ball past Darren Randolph.
Motherwell had a loud penalty shout five minutes later when John Rankin appeared to handle on the edge of the box, before Russell curled a shot just over the crossbar at the other end.
And Dundee United had a half-chance to double their lead just after the break but Brian McLean shot over the crossbar.
Motherwell then had a period of pressure but were caught on the counter-attack once again and Randolph did well to prevent Mackay-Steven scoring from a tight angle.
Motherwell's Kallum Higginbotham then shot straight at Radoslaw Cierzniak but Randolph was soon very busy at the other end, denying Mackay-Steven and Rankin in quick succession.
Russell was then put through one-on-one with Randolph but the Motherwell goalkeeper saved once more and Mackay-Steven put the rebound over.
The woodwork then came to the rescue of Dundee United, Nicky Law's lob bouncing back off the crossbar after Cierzniak had punched the ball out to him.
But it was the visitors who came closest in the final 10 minutes, Jon Daly's header having to be cleared off the line by Shaun Hutchinson, who then repeated the feat from a Mackay-Steven shot.
James McFadden made a late appearance from the bench, having re-joined Motherwell on Monday, but could not prevent his side from suffering a first home defeat of 2013.