Ospreys fly-half Dan Edwards kicked a brilliant 80th-minute drop-goal to clinch a dramatic victory against Ulster.

Edwards kicked 14 points with centre Keiran Williams scoring the hosts' solitary try.

Ulster had scored tries from Marcus Rea and Tom Stewart with Nathan Doak adding two conversions.

The winning kick crowned a momentous week for Edwards with the 20-year-old also signing a new Ospreys deal.

The victory in front of a crowd of 5,093 in Swansea lifts Ospreys to seventh in the United Rugby Championship (URC) table while Ulster are eighth.

Captain Justin Tipuric returned from a broken thumb suffered in November, while prop Nicky Smith recovered from a shoulder problem.

Lock Victor Sekekete and centre Evardi Boshoff made their debuts after joining from South African side Cheetahs but Wales quartet George North, Gareth Thomas, Adam Beard and Owen Watkin were not released from the Six Nations squad.

Ireland coach Andy Farrell released Iain Henderson, Jacob Stockdale and Nick Timoney who all started, while Stewart was on the bench, but Stuart McCloskey and Tom O'Toole were retained.

There was a late Ulster change with wing Mike Lowry failing to make it through the warm-up and replaced by Ethan McIlroy with Robert Baloucoune coming onto the bench.

Edwards missed an opening penalty attempt, while Ulster almost gained an inventive first try but wing Stockdale could not collect a clever Nathan Doak cross kick.

The home scrum was dominant in the first half with Ulster forced into a front-row change as injured prop Marty Moore was replaced by Scott Wilson.

Edwards finally opened the scores in the 30th minute with a penalty before Ulster suffered a blow by losing injured captain Henderson with a toe injury.

It will be a Six Nations injury concern although Ireland still have the likes of locks Tadhg Beirne, Joe McCarthy and James Ryan available next weekend.

Ulster shrugged off the forward disruption and demonstrated a clinical nature the Ospreys had not in the first half with flanker Rea burrowing over and Doak converting.

Edwards slotted over a second penalty to reduce the deficit to one point as a forgettable first half concluded, a 40-minute contest littered with handling errors from both sides.

Flankers Tipuric and Harri Deaves had an excellent start to the second half with some tigerish tackling and trademark turnovers.

Their back-row colleague Morgan Morse was shown a yellow card by Italian referee Federico Vedovelli for a deliberate knock-on.

South Africa's two-time World Cup winner Steven Kitshoff was introduced from the Ulster replacements bench.

Ospreys coped admirably with Ulster having the extra man by repelling the Ulster forward attacks and Edwards kicked a third penalty as the home side regained the lead.

The hosts were reduced to 13 men when lock James Ratti was adjudged to have tripped Ulster fly-half Flannery. Ulster capitalised as Stewart was driven over with Doak converting from the touchline.

The teams were evened up at 14 men with the return of Morse while Ulster replacement Luke Marshall was shown a yellow card after only being on the field for a minute.

Ospreys temporarily threatened but the move broke down and a huge kick from Stewart relieved the pressure.

The home side responded with a counter-attacking try from almost their own line that was intercepted by Jack Walsh before linking with Mat Protheroe who released Edwards.

The Ospreys fly-half was chased down by his opposite number Flannery but found the supporting centre Williams who cantered over to score.

Edwards converted before Wales wing Alex Cuthbert came on as a replacement for his first game in a year after a turbulent time with injuries.

Ospreys replacement flanker Will Hickey was penalised for a no-arms tackle with Flannery slotting over what looked like a match-winning penalty.

This was before Edwards' intervention as he was mobbed by his team-mates after clinching a fifth successive victory in all competitions for Ospreys.

Ospreys head coach Toby Booth: "The good thing about that whole drop-goal episode was Dan initiated the whole thing.

"We have a drop goal routine for exactly those moments but it's one thing having it, it's another thing doing it.

"Ultimately, the quarterback is the quarterback and to have the self-belief, skill and execution to do it, those pressure moments are important.

"One of our buzz phrases is we talk about going all in and Dan went all in. That's a great example of that. He is developing into a fine player."

Ulster head coach Dan McFarland: "The game was pretty scrappy in the first half and we looked a little bit rusty after the break. Ultimately the game came down to two instances, both of where we were in control.

"One in their 22 where they got an intercept pass and the second one was at the end of the game when we were in total control and the referee called a scrum on the back of a maul. I have literally no idea of what that was about.

"I'm going to ask and find out, because ultimately those two instances decided the game in the Ospreys favour."

Ospreys: Jack Walsh; Mat Protheroe, Evardi Boshoff, Keiran Williams, Keelan Giles; Dan Edwards, Reuben Morgan-Williams; Nicky Smith, Sam Parry, Tom Botha, James Ratti, Victor Sekekete, Harri Deaves, Justin Tipuric (capt), Morgan Morse.

Replacements: Lewis Lloyd, Rhys Henry, Ben Warren, Lewis Jones, Will Hickey, Cameron Jones, Alex Cuthbert, Tom Florence.

Ulster: Will Addison; Ethan McIlroy, James Hume, Jude Postlewaithe, Jacob Stockdale; Jake Flannery, Nathan Doak; Andrew Warwick, John Andrew, Marty Moore, Harry Sheridan, Iain Henderson (capt), David McCann, Marcus Rea, Nick Timoney.

Replacements: Tom Stewart, Steven Kitshoff, Scott Wilson, Cormac Izuchukwu, Matty Rea, Dave Shanahan, Luke Marshall, Rob Baloucoune.

Referee: Federico Vedovelli (FIR)

Assistant referees: Maickel English & Carwyn Williams (WRU)

TMO: Matteo Liperini (FIR)