LONDON (REUTERS) - Manchester United manager Louis van Gaal was frustrated his side "forgot to score" against Swansea City but believes they were unlucky to lose 2-1 in the Premier League on Saturday.

United's scratchy performances this season have received criticism but Van Gaal insisted on Friday that his team would be top of the Premier League based on their form since November.

United did little to support their manager's claims at the Liberty Stadium, however, as they failed to convert their chances, handing Swansea a double over Van Gaal's side after their win at Old Trafford in the first game of the season.

"Of course you can say we dominated the game but the only thing we could have done more was score more out of the chances we created," Van Gaal told the BBC.

"We were the unlucky team. I think we created enough chances. We were the dominant side in both halves.

"Possession is good but your purpose is to score goals and we have created many chances but then you have to score.

"Today we played well - only we forgot to score. We have to be more effective."

Ander Herrera's precise drive into the bottom corner gave United the lead but Ki Sung-yueng equalised before Bafetimbi Gomis turned in Jonjo Shelvey's long-range strike late on to give Swansea the victory.

"Conceding so quickly after opening the scoring was important," Van Gaal said. "It was a throw in for Swansea and we should have been more organised. But it was a good goal by Swansea.

"I think it was our best second half, we created a lot of chances and dominated the game but we don't score and then they score out of a Sunday shot that deviated."

United dropped to fourth in the table with 47 points from 26 matches after only their second loss in 20 matches in all competitions.

"I have said to my players that you have done what I have said except score out of the many chances we have created," Van Gaal told reporters.

"It is very disappointing but in the process of the development of our play then it was a very good match.

"To play like this, so dominating, creating chances, you can hardly improve apart from scoring goals, but that is also a bit of luck."