Cardiff Blues were beaten 11-7 at a wet and windy Rodney Parade as Ulster won their fourth consecutive Pro14 match.
The Welsh went ahead, against the run of play, with a try by Rey Lee-Lo, who was carried off in the second half.
Michael Lowry crossed for the visitors with the last play of the first half to give Ulster a 8-7 lead at the break.
John Cooney's second penalty was the only score in the second half, maintaining Ulster's unbeaten start.
Ulster climb to the top of Conference A while Cardiff Blues, who have now won two and lost two, remain second in Conference B.
Blues had Wales back-row Josh Turnbull back from suspension following a frustrating defeat to Munster last time out, while Will Boyde returned after injury.
Ulster had fly-half Billy Burns back from injury to captain the side alongside scrum-half John Cooney, who had been released to play by Ireland, while flanker Matty Rea made his 50th appearance for the Irish province.
The Irish visitors started the game strongly with their forwards carrying hard. Their sustained pressure was rewarded with Cooney slotting a penalty after Will Boyde was penalised at a ruck on 16 minutes.
The hosts responded well and seven minutes later crossed for the evening's opening try, excellently taken, during a rare foray into their opponents' half.
From a lineout midway inside the Ulster half, the Blues went through a couple of phases before Jarrod Evans put in a perfectly placed chip for Lee-Lo to pounce on and cross to score, with Evans converting.
Mounting penalties
Ulster then controlled the rest of the first 40 minutes with virtually all the territory and possession, forcing Blues to defend phase after phase of attack.
With replacement Olly Robinson in the sin-bin, and paying the price for a mounting penalty count, the visitors' dominance was finally rewarded with full-back Lowry picking up a loose ball to dance through.
Cooney missed the fairly straight-forward conversion, which meant Ulster's lead was just one point at half-time.
Blues started the second period positively and gained a foothold in the visitors' half, but were left empty-handed as Evans pulled a penalty attempt wide.
With the game evenly poised as the final quarter approached there were worrying scenes, with Lee-Lo stretchered off after taking a heavy bang to the head in making a tackle on Luke Marshall.
The game opened up somewhat in the latter stages with both sides trying to show adventure as the conditions improved, but ultimately it was Cooney's boot that proved the difference as he slotted a penalty on 64 minutes after a breakdown offence by Blues.
Despite both sides' efforts that was the final score of the game and as the Irish side maintained their 100% start to the season, Cardiff Blues had to settle for a losing bonus point.
Cardiff Blues: Matthew Morgan; Aled Summerhill, Rey Lee-Lo, Willis Halaholo, Hallam Amos; Jarrod Evans, Lewis Jones; Corey Domachowski, Kristian Dacey (capt), Dmitri Arhip, James Ratti, Rory Thornton, Josh Turnbull, Jim Botham, Will Boyde.
Replacements: Ethan Lewis, Brad Thyer, Scott Andrews, Ben Murphy, Ollie Robinson, Jamie Hill, Jason Tovey, Garyn Smith.
Ulster: Michael Lowry; Craig Gilroy, Stewart Moore, Stuart McCloskey, Louis Ludik; Billy Burns (capt), John Cooney; Eric O'Sullivan, Adam McBurney, Marty Moore, Alan O'Connor, Kieran Treadwell, Matty Rea, Jordi Murphy, Nick Timoney.
Replacements: John Andrew, Jack McGrath, Ross Kane, Sam Carter, Sean Reidy, Alby Mathewson, Luke Marshall, Ethan McIlroy.
Referee: Sam Grove-White (SRU)
Assistant Referees: Adam Jones, Ben Breakspear (both WRU)
TMO: Ian Davies (WRU)