Manchester United kicked off their Premier League season with a promising win over Leicester City. Unfortunately for them, the promise was short lived as they lost 3-2 to Brighton. Glenn Murray, Shane Duffy, and Pascal Gross were the goal scorers for Brighton. As for United, Romelu Lukaku and Paul Pogba were on the score sheet.Brighton went ahead in 25 minutes when Solly March whipped in a first-time cross which was flicked on by Glenn Murray, and Brighton took the lead. Almost immediately, Brighton scored their second when United failed to clear a corner. The ball eventually fell to Shane Duffy, the center half not known for his goal scoring took a shot which went past De Gea onto the back of the net.United responded to this when a Luke Shaw shot found its way to Romelu Lukaku who headed home from close range. United would have taken 2-1 at the break, but that was not to be as Bailly made a reckless tackle in the box which led to a penalty. Gross took the penalty, and sure enough he scored.Mourinho made a double change at half-time by replacing Mata and Andreas Pereira with Marcus Rashford and Jesse Lingard. He eventually ended up going more direct by sending Marouane Fellaini on. Unfortunately for him, nothing seemed to work. Pogba ended up scoring a penalty in injury time, but that was a mere consolation as Brighton held on to their one goal advantage.This was a great win for Brighton, but it raises a lot of questions for Manchester United's title aspirations. Man Utd did not have a good pre-season, and Jose Mourinho has publicly talked about not having a good transfer window. This loss came on a day Manchester City humiliated Huddersfield by scoring 6 goals.If Manchester United want to challenge for the title or even challenge for the top 4, they may have to improve quickly or else they may be left behind. It is worrying for Manchester United fans to see their team not perform to their potential.Here are the best Twitter reactions to the humiliating loss for Jose Mourinho and his men.There are so many talented players at Manchester United that already look totally fed up and it's only the second game of the season. This is going to be a turbulent year.— Liam Canning (@LiamPaulCanning) August 19, 2018Mourinho’s 3rd season looks like following a familiar pattern.— Gary Lineker (@GaryLineker) August 19, 2018Manchester United do really Brighton up my day!— Aadam (@aadambirmingham) August 19, 2018Manchester United created just four chances against Brighton, the fewest they have created against a team outside of the 'top six' since the start of last season.Struggling in the final third. 😕 pic.twitter.com/hjUh87ws67— Squawka Football (@Squawka) August 19, 2018Graeme Souness: “Manchester United didn’t become one of the biggest clubs in the world playing football that teams in the third and fourth division were playing 30/40 years ago.” #MUFC— Emma Sanders (@em_sandy) August 19, 2018It was so obvious that Manchester United needed to address the full back areas, right wing and center-back in the summer. If Ed Woodward doesn’t trust the manager then he should sack him.— Mootaz Chehade (@MHChehade) August 19, 2018My timeline packed with negative comments about @ManUtd who look in a total mess. However, I’ll take a different angle. Bravo Brighton!! Brilliant spirit, a famous win, well done CH. impressed, but not surprised👏👏— Jake Humphrey (@mrjakehumphrey) August 19, 2018Who to appoint if Mourinho is sacked doesn’t even matter, he just needs to get out of Manchester United immediately.— Rafael Hernández (@RafaelH117) August 19, 2018Waiting for post match comments from Manchester United manager Ed Woodward. #MUFC— Naveen Ullal (@UllalIBT) August 19, 2018Manchester United not just beaten by Brighton. They were out-thought, out-hustled, outplayed. Like watching a Bully being bullied. Biff Tannen punched in the chops by George McFly— roger bennett (@rogbennett) August 19, 2018