Paddy Jackson's penalty was all that separated the sides after a tight first period that belonged to the defences.

But after another nip-and-tuck second half which saw AJ MacGinty level the scores, Williams was set up by Luke Marshall - who had earlier seen yellow - for the game's decisive try that handed Pat Lam's troops their first defeat at home all season.

It was the high-flying Connacht who started the brighter side at the Sportsground, forcing some early pressure inside the Ulster 22 with Jack Carty kicking a penalty to the corner on four minutes.

Lam's side looked for the catch-and-drive, but Ulster stood firm before Carty's kick through was collected and the visitors were able to clear.

Ruan Pienaar caught Kieran Marmion in possession after 14 minutes and Paddy Jackson was able to kick for touch inside the Connacht 22 with the hosts penalised for holding on.

But skipper John Muldoon earned the turnover for his side getting in over the ball to relieve the pressure.
Neither side could force themselves into the ascendency with both defences winning crucial penalties or forcing knock-ons inside their own territory.

The first real scoring opportunity came on 29 minutes when Connacht's numbers forced a penalty 15 metres outside the Ulster 22, but Craig Ronaldson's effort off the tee was both short and wide of the posts.

And Ulster punished their hosts, who were penalised for hands in the ruck three minutes later, and Jackson slotted his kick from ten metres inside the touchline to make it 3-0.

The visitors looked to add to their tally before half-time, and with Connacht pinged at the breakdown once more Ulster were able to kick to touch inside the 22.

But that line-out was turned over and Niyi Adeolokun was able to clear to keep it very tight at the interval.

Connacht began the second half in the ascendancy, with Tiernan O'Halloran and Adeolokun making key breaks, but the latter was hauled into touch.

Lam's side were dominating both the possession and territory, and were handed a golden opportunity to draw level after 48 minutes with Ulster off their feet on the 22, but again Ronaldson's kick was wide - shaving the left upright.

Ulster spurned a golden try-scoring opportunity when Marshall's pass fell short of Andrew Trimble who was in space on the right wing, but momentum seemed to switch towards Connacht with the introduction of MacGinty after 56 minutes.

He almost made an immediate impact with a chip through for Bundee Aki and Marmion to chase, but in the aftermath Marshall saw yellow via the TMO for a deliberate trip on the 25-year-old.

And with Ulster a man down, Connacht made their advantage count, winning a penalty at the scrum for MacGinty to level the contest from the tee.

Ulster were soon back to full strength and began to go through the phases as the game entered the final ten minutes protecting possession well, and after a brilliant scrum the room was there for Marshall to charge towards the line before setting up Williams to score.

Jackson added the extras, and while Connacht had the opportunity to run the ball back at Ulster, they were turned over on halfway meaning they still have just one win in their last 19 clashes with their Irish rivals.

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