Erik ten Hag's reign as Manchester United manager got off to a nightmare start as Brighton registered their first ever victory at Old Trafford with a 2-1 win on the opening weekend of the Premier League season.
Alexis Mac Allister's own goal gave United a foothold in the game, but they rarely looked like getting back on level terms, showing the scale of the task lying ahead for Ten Hag.
The former Ajax boss left Cristiano Ronaldo on the bench after he only returned to pre-season training last week but without him, United had no focal point to their attack as Christian Eriksen started in an unfamiliar role as a false nine.
Brighton exposed the same flaws in United's wide open midfield to pick apart Ten Hag's men with ease.
Danny Welbeck, who United discarded back in 2014, was a constant threat in behind the vulnerable defensive pairing of Harry Maguire and Lisandro Martinez.
Welbeck created the opener as he ran off Maguire and laid the ball across goal for Gross to slot into an unguarded net at the back post.
Ronaldo's introduction early in the second half at least lifted the noise levels inside Old Trafford.
Marcus Rashford looked reborn during pre-season, but failed to make his mark when it counted as Robert Sanchez produced a stunning save to block the England international's effort from Ronaldo's pinpoint cross.
Sanchez gave United a lifeline 22 minutes from time, flapping at a corner under pressure from Diogo Dalot and then slapping the ball into his own net off Mac Allister, but it was not enough.
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