Scarlets claimed just a second United Rugby Championship victory of the season as they overcame Dragons despite having Sione Kalamafoni sent off before half-time.

Angus O'Brien and Lewis Jones crossed for Dragons, who could not capitalise on Kalamafoni's dismissal for punching.

Scarlets were the better side in the second half and deservedly triumphed.

It was a disappointing first return to Parc y Scarlets for Dai Flanagan, who ended an eight-season spell on the west Wales region's coaching staff when he took charge at Dragons last summer.

His side were left ruing their failure to push on after scoring their second try - and establishing a four-point lead - moments after Kalamafoni was sent off following a clash with Ross Moriarty.

Scarlets remain 15th in the table, though they close the gap on Dragons - who are 14th - to only four points having won in the URC for the first time since October.

Both sides came into the contest on the back of Boxing Day disappointment, with Scarlets going down at Ospreys and Dragons beaten in agonising fashion by a last-gasp Cardiff try.

It was Scarlets who made an early impression as they returned to home turf, with Kalamafoni denied what looked like the opening score because of a knock-on in a ruck before Leigh Halfpenny kicked two early penalties.

Scott Williams then made a promising break only to pick up an injury in the process which ended his night, with Dragons getting on the board through a JJ Hanrahan penalty after Aaron Shingler was penalised for not rolling away.

Dragons claimed the evening's first try when Rio Dyer juggled a pass and then sliced through a gap in the home defence before sending former Scarlet O'Brien over in the corner.

Hanrahan added the extras from the touchline to make it 10-6, but Scarlets swiftly reclaimed the lead when some sweet handling from forwards and backs ended with Halfpenny supplying the scoring pass for Evans.

After Halfpenny's successful conversion, tempers flared when Sam Lousi tangled with Ashton Hewitt on the touchline.

Scarlets number eight Kalamafoni needlessly got involved - and ended up throwing punches at Moriarty after the Wales back row had pulled his scrum cap.

Moriarty saw yellow for his actions, while Kalamafoni became the fourth Scarlets player - and the second in as many games - to be sent off this season.

Dragons kicked the ensuing penalty into the corner before a clean catch and drive at the lineout allowed scrum-half Jones to race over the line.

Hanrahan's conversion made it 17-13, though Halfpenny's third successful penalty meant there was just a point in it at half-time.

Dragons were restored to 15 men when Moriarty returned from the bin two minutes into the second period, yet Scarlets regained the lead thanks to another Halfpenny penalty after Matthew Screech was penalised for not rolling away.

Scarlets seemed untroubled by their numerical disadvantage, Dwayne Peel's team playing with courage and composure as they claimed their second try just before the hour mark.

After winning a scrum deep in Dragons territory, Scarlets went through the phases before Blacker spotted a gap in the visitors' defence and scampered under the posts to mark his 50th appearance for the region with a try.

The immaculate Halfpenny was successful once more with the conversion.

Hanrahan missed the chance to reduce the arrears with a poorly struck penalty, before Scarlets dug in to hold onto their advantage against a Dragons side who offered little attacking threat as the contest went on.

Scarlets sent the majority of the 8,556 crowd home happy as a Dan Davis turnover led to McNicholl diving over in the corner in the last play of the game.

Scarlets head coach Dwayne Peel:

"It's very pleasing. We started brightly and when we had the ball I felt we were causing problems, but second half I was really pleased with our defensive effort because we were really physical and turned some good ball over.

"It was nice for us to score a try from our defence, that last one - a turnover and a good finish.

"Obviously we were disappointed [at half-time] to be down to 14 again, but it wasn't a case of feeling sorry for ourselves. We had a job to do and we did it."

Peel on the red card:

"You can't be punching, can you? I have no arguments. I was disappointed with the way it started and obviously escalated on the back of that.

"Discipline is a definitely an issue because we have had four red cards this year. We know the rules - you can't be punching, regardless of who started it or what happened that led to that."

Dragons head coach Dai Flanagan:

"No-one said it would be easy and that's a big step backwards for us tonight. We lost all the collisions, all the 50-50s, and we can't afford to do that.

"I am a bit disappointed because collectively we didn't really stick to the script and we have got to look at why.

"Sometimes [the extra man] can work for you, sometimes against you. There are 15 different minds on the field. I have to look at connecting that and we didn't quite get that right.

"It's a physical game rugby and emotion just took over [in the red card incident]. I know Kalamafoni pretty well and he's a great human being, so I am pretty sure there was no poor meaning in it, if that makes sense."

Scarlets: Leigh Halfpenny; Johnny McNicholl, Joe Roberts, Scott Williams, Steff Evans; Rhys Patchell, Dane Blacker; Kemsley Mathias, Ken Owens (capt), WillGriff John, Vaea Fifita, Sam Lousi, Aaron Shingler, Dan Davis, Sione Kalamafoni.

Replacements: Shaun Evans, Steff Thomas, Sam Wainwright, Morgan Jones, Carwyn Tuipulotu, Kieran Hardy, Dan Jones, Jonathan Davies.

Dragons: Angus O'Brien; Rio Dyer, Steff Hughes (capt), Sio Tomkinson, Ashton Hewitt; JJ Hanrahan, Lewis Jones; Aki Seiuli, Bradley Roberts, Chris Coleman, Joe Davies, George Nott, Aaron Wainwright, Taine Basham, Ross Moriarty.

Replacements: Brodie Coghlan, Rob Evans, Luke Yendle, Matthew Screech, Ben Fry, Che Hope, Sam Davies, Max Clark.

Referee: Ben Whitehouse (WRU)

Assistant referees: Craig Evans & Mike English (WRU)

TMO: Sean Brickell (WRU)