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| Ryan Giggs and Louis Van Gaal. |
The Red Devils were beaten 2-1 away at the Liberty stadium, with Swansea doing the double over them thus season.
And the Dutch tactician said their inability to find the net cost them in the match, despite dominating their opposition.
"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. Today we were the unlucky team. I think we created enough chances. We were the dominant side in both halves.
"Conceding so quickly after opening the scoring was important. It was a throw in for Swansea and we should have been more organised. But it was a good goal by Swansea.
"We played well - only we forgot to score. We have to be more effective," van Gaal said.
Meanwhile, League leaders Chelsea ended a turbulent week with a disappointing 1-1 home draw against strugglers Burnley.
The build-up to the game was overshadowed by the fallout from an incident in Paris on Tuesday in which a group of Chelsea fans prevented a black man from boarding a Metro train while chanting racist songs.
Chelsea took an early lead through Branislav Ivanovic, but after Nemanja Matic had been sent off for lashing out at Ashley Barnes, Ben Mee headed in an 81st-minute equaliser.
Ivanovic struck in the 14th minute, finishing from six yards after Eden Hazard had weaved his way through a posse of defenders on the Chelsea right.
But the tide began to turn in the 70th minute when Ivanovic's countryman Matic was sent off for shoving Barnes to the ground after the Burnley midfielder caught him on the shin with an ugly challenge.
Eleven minutes later, the visitors claimed a scarcely hoped-for draw when Mee headed home Kieran Trippier’s left-wing corner at the back post to nudge Sean Dyche's side closer to safety.
Arsenal capitalised on United's slip-up with a 2-1 win at London rivals Crystal Palace that saw Arsene Wenger's side climb to third place in the table.
Santi Cazorla opened the scoring in the eighth minute with a penalty and Olivier Giroud added a second on the stroke of half-time, following up after Julian Speroni had saved from Welbeck, but the England forward looked to have been offside in the build-up.
Glenn Murray tapped in a stoppage-time consolation for Palace.
Elsewhere, Tim Sherwood began his tenure as Aston Villa manager with a cruel 2-1 loss at home to Stoke City that saw his new side slip below Burnley to second-bottom.
Scott Sinclair headed Villa in front in the 20th minute, but Mame Biram Diouf equalised and Victor Moses gave Stoke victory with a stoppage-time penalty after Ron Vlaar was dismissed for felling Diouf.
Perennial troublemaker Joey Barton was sent off for flinging a hand towards Tom Huddlestone's nether regions as Queens Park Rangers lost 2-1 at relegation rivals Hull City.
Nikica Jelavic volleyed Hull ahead and although Charlie Austin headed in a 39th-minute equaliser shortly after Barton had been given his marching orders, Dame N'Doye gave Hull victory with an 89th-minute header.
In the day's other game, Sunderland and West Bromwich Albion played out a drab 0-0 draw at the Stadium of Light.
Chelsea manager Jose Mourinho had a face of thunder in his post-match interview. He had notes of four key incidents, but would not talk about any of the incidents. "I am punished when I refer to these situations and I don't want to be punished."