The new Manchester United era under Dutch coach Louis van Gaal suffered its first bruise after enduring their first defeat at home on the opening day of the league season since 1972.
Goals from Ki Sung-Yueng and Gylfi Sigurdsson handed Swansea a 2-1 win over the Red Devils in an English Premier League match at Old Trafford on Saturday.
United were the better side for the majority of the half and dominated the possession stakes, but some slack defending saw them a goal down after the opening 45 minutes.
The Red Devils dictated the flow of play, but struggled to find the right pass in the final third that would lead to a goal.
In fact, the first shot on goal came in the 12th minute from Swansea when Sigurdsson let fly from 24-yards out, but David De Gea produced a good save.
Ten minutes later United suffered a bit of a set-back when Jesse Lingard had to leave the field injured and was replaced by Adnan Januzaj.
In the 25th minute the home side created their first decent effort on goal when a swift passing movement saw Phil Jones with a shot from an acute angle on the right side of the box, but the keeper produced a great save to deny him.
Three minutes later, very much against the run of play, Swansea took the lead when Ki Sung-Yueng found the bottom right corner of the net from the edge of the box, 1-0.
Despite going behind, United continued to govern proceedings, but were unable to find the break through before the end of the half.
Eight minutes into the second half, however, and United did find the equaliser when Wayne Rooney acrobatically turned home a flicked on corner-kick from a couple of yards out, 1-1.
In the 66th minute the Red Devils came close to taking the lead when a 24-yard free-kick from Rooney struck the outside of the right-hand post.
Six minutes later, again against the run of play, Swansea took the lead for the second time when Sigurdsson made the most of a miscued effort from Wayne Routledge to poke the ball home from ten-yards out, 2-1.
United tried to find their way back into the match, but were unable to do so as they suffered their first loss of the league season in the opening game.