Van Gaal victorious in Old Trafford opener
The Dutch boss, who took over after leading the Netherlands to third place at the World Cup last month, was left with plenty to ponder ahead of Saturday's Premier League opener against Swansea.
Wayne Rooney, captain for the night, missed a penalty but Darren Fletcher drove in United's opener shortly after the interval only for Rodrigo to equalise in the 71st minute before Fellaini scored his first goal in United colours.
Van Gaal, given the task of returning United to winning ways after David Moyes, Alex Ferguson's chosen successor was sacked towards the end of a season where the club finished seventh in the Premier League, received a huge cheer as he emerged from the tunnel to supervise the warm-up.
He also endeared himself to the United fans by greeting lots of them at the front of the South Stand as he made his way to the dug-out after half-time.
With Robin van Persie, Danny Welbeck, Jonny Evans, Antonio Valencia, Nani, Anderson and Wilfried Zaha, as well as the injured Michael Carrick, among those watching from the stands, van Gaal selected a makeshift side.
Defender Tyler Blackett, who has featured regularly throughout pre-season, started as one of three centre-backs, with Ashley Young and Reece James playing as wing-backs.
Although under less pressure, the defence retained the ball far better than in their recent 3-1 friendly win over Liverpool.
Ander Herrera, making his first home appearance since joining from Athletic Bilbao, impressed with his willingness to dictate play sitting in front of the back four.
- Valencia's sharp start -
But van Gaal will want to see much more from his new team when the competitive action starts on Saturday.
Nuno Santo's Valencia do not begin their La Liga campaign until they face Sevilla on August 23 but they started with the greater impetus, midfielder Sofiane Feghouli driving over from distance in the early stages.
The visitors looked sharp on the break and after Herrera was robbed by Feghouli, Rodrigo's clever pass put the midfielder through only for Feghouli to shoot straight at David de Gea.
United had the chance to move in front when a great ball from Herrera picked out Young and the wing-back's first time cross looked set to be headed in by Rooney only for the forward to go down dramatically under Antonio Barragan's challenge.
The England striker struck the spot-kick against the post but United took the lead three minutes into the second half.
Young's corner was flicked on by Mata and Fletcher's deflected effort from the edge of the area beat goalkeeper Diego Alves.
Valencia almost drew level when Rodrigo found space behind the United defence but defender Phil Jones pulled off an impressive sliding challenge to divert the ball.
But with just under 20 minutes remaining, the visitors did manage an equaliser when Tom Cleverley, one of several United substitutes on just after the hour mark, failed to deal with a whipped Pablo Piatti free-kick that Rodrigo turned in at the far post.
Valencia should have had a second goal when Piatti turned the ball past the near post after getting on the end of Rodrigo's cross.
United substitute Adnan Januzaj opened up the Valencia defence with a sliding pass only for Rooney to lift his shot over from 20 yards.
Fellaini is reportedly facing an uncertain future at United, a year after he joined from Everton, but he controlled a long ball forward from Blackett before rolling his shot into an empty net.
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