United dominated possession but failed to register even a single shot on target, the first time in a home league game since May 2009, allowing Southampton to prevail through Dusan Tadic's 69th-minute strike.
Victory took Ronald Koeman's side above United into third place, but Van Gaal, who fell out with Koeman during their time together at Ajax, felt the visitors were fortunate to leave Manchester with all three points.
"We played a much better game than Southampton," the Dutchman told the BBC after United's 11-game unbeaten run came to an end. "They were lucky to score out of nothing. We didn't create so much, but we dominated the game. They came for a draw, I believe, and they go away with a victory. That is disappointing."
Skipper Wayne Rooney also felt the home side did not deserve to lose. “That is football, that is how it goes,” he said. “I think overall we had the better chances and played the better football and deserved to win, but we were punished.”
On the other hand, Southampton manager Koeman was pleased to see his side prevail, having seen them beaten 2-1 by United in December's reverse fixture despite bossing the game.
“Juan Mata had two big chances at the end. We missed that luck in the home game and we got that today,” he said. “If you play against a big side, you need spirit and quality, but you also need belief in yourself and your teammates and we showed that today.”
Like Sports on Facebook, follow @ETribuneSports on Twitter to stay informed and join in the conversation.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ