Les Kiss' men were stopped from their sixth consecutive win of the Pro12 season
Ulster found themselves up against a reinvigorated Connacht, who inflicted their first defeat of the season at the Galway Sportsground, winning their Guinness PRO12 clash 30-25.
A triple try salvo in the first half from the defending PRO12 champions set the platform for them, with Cian Kelleher in top form, scoring twice in the hosts' bonus point win.
Ulster will take a losing bonus point home, but it's scant consolation for Les Kiss' men who will be disappointed their unbeaten run has come to an end in this fashion.
It took the defending champions all of two minutes to open their account as fly-half Jack Carty found a huge amount of space in the Ulster defensive line and managed to jink through and under the posts for the score.
It was the exact opposite start to what Ulster wanted, but they did rally and Jackson opened their account with a penalty five minutes later.
Indeed, for all the dominance Ulster showed early on, it was surprising at they didn't manage to score any more points, but the work from Connacht at the breakdown was preventing the visitors from breaking through.
Instead it was down to the hosts to show them the way to the try line as they continually battered away at the Ulster defensive line and eventually the gap appeared with Tiernan O'Halloran floating a beautiful pass over the head of Tommy Bowe for Cian Kelleher to score.
A minute later and they had their third try. Bowe misjudged the kick off, allowing Connacht to gather and break, eventually leading to substitute flanker James Connolly taking the ball at pace and crashing over.
All of a sudden Les Kiss' men had fallen 19 points behind, but they didn't panic and used their forward advantage to take a set of mauls into the corner, which led to Craig Gilroy finding the space in the corner to cross.
In amongst all the mauls Connacht prop Conor Carey saw yellow for repeated infringements, but Carty extended the hosts' lead just before the break with a penalty.
But after the break it was all Ulster as they scored two quick tries to level the scores, the first of which came from their dominant forward platform as they set up a driving maul which crashed over, Rory Best the benefactor.
Then came an excellent score which levelled it at 22-all, Paul Marshall drawing the defender from the back of a scrum and releasing Tommy Bowe who gave it inside to Jared Payne for the try.
From there it looked like the momentum would only turn the game one way, but Connacht hit back within the 50 minute mark as man of the match Kelleher again crossed the whitewash for the bonus point try after the space became available out wide.
Carty missed the conversion, but then added a penalty to stretch the Galway men's lead back to beyond a converted score, but Jackson quickly erased that with a penalty of his own to bring the lead back to five.
With ten minutes to go, the Ulstermen made a big call not to go for the posts when awarded a penalty and instead opted to go for the corner, a decision which cost them as they failed to get the go ahead try.
Instead it was left to Pat Lam's men to hold out, aided by Ross Kane's yellow card for a shoulder charge with six minutes to play, giving them a hard fought victory and condemning Ulster to their first defeat of the season.
The scorers
For Connacht
Tries: Carty, Kelleher (2), Connolly
Cons: Carty (2)
Pens: Carty (2)
For Ulster
Tries: Gilroy, Best, Payne
Cons: Jackson (2)
Pens: Jackson (2)
CONNACHT RUGBY
(15-9) Tiernan O'Halloran, Niyi Adeolokun, Bundee Aki, Craig Ronaldson, Cian Kelleher, Jack Carty (Shane O'Leary 71), Caolin Blade; (1-8) Finlay Bealham (Ronan Loughney 60), Dave Heffernan (Shane Delahunt 72), Conor Carey (JP Cooney 60), Ultan Dillane, Andrew Browne (Lewis Stevenson 67), Eoin McKeon (James Connolly 8), Jake Heenan, John Muldoon.
Subs not used: Stephen Kerins, Stacey Ili.
Yellow card: Conor Carey (32')
ULSTER RUGBY
(15-9) Jared Payne, Tommy Bowe, Louis Ludik (Brett Herron 63), Darren Cave (Rob Lyttle 40), Craig Gilroy, Paddy Jackson, Paul Marshall; (1-8) Callum Black (Andy Warwick 54), Rory Best (Rob Herring 61), Rodney Ah You (Ross Kane 55), Robbie Diack, Peter Browne (Kieran Treadwell 61), Iain Henderson, Clive Ross, Roger Wilson (Sean Reidy 54).
Sub not used: David Shanahan.
Yellow card: Ross Kane (74')
Man of the Match: Cian Kelleher (Connacht)
Attendance: 6,194
Referee: Gary Conway (IRFU)