Skipper Harry Maguire made a “nightmare start” as Pascal Gross struck twice to give Brighton their first win at Old Trafford in 113 years. 4 Erik ten Hag knows he has a job on his hands after Man Utd were stunned by BrightonCredit: Reuters 4 Ten Hag warned fans there will be no quick fix after watching the side flop against BrightonCredit: Rex New boss Ten Haag pointed to costly individual mistakes and warned fans that the team’s problems cannot be quickly reversed. The Red Devils were booed at half-time, while there were more jeers at the end despite an improved second half. Ten Haag said: “It’s a hell of a job. “It’s definitely a setback. It’s a real disappointment and we have to deal with it. “I’m not completely satisfied because we’re losing and it’s not necessary. We should have done things better. “We gave away two easy balls and the organization was a big mistake. We clarified how to deal with situations. It was unnecessary. “We have to take the lessons and learn quickly from this. We don’t have time and we have to deliver.” Ten Haag defended his decision not to start Cristiano Ronaldo, who declared himself ready to start on the eve of the match. FREE BET AND SIGN UP OFFERS – BEST NEW CUSTOMER OFFERS The former Ajax boss has selected debutant Christian Eriksen to lead the line — with Anthony Martial out injured. United improved after Ronaldo was introduced in the 52nd minute and pulled one back with an own goal from Alexis McAllister. The United boss said: “Cristiano is now maybe ten days into team training and too short for 90 minutes. You can’t force it.” Maguire and new centre-back partner Lisandro Martinez had a difficult afternoon against former United man Danny Welbeck. Maguire said: “It was a nightmare start to be 2-0 down at half-time. “It’s the worst possible start. It wasn’t good enough. “It’s definitely a setback. It’s a real disappointment and we have to deal with it.” Eric ten Haag “We hit and puffed and got one back — but it’s a bad start. “The first goal hit us very badly. They had a lot of control.” United fans demonstrated outside the stadium before kick-off with a huge banner that read: “Fight Greed, Fight United, Fight Glazer.” And frustrations spilled into the stands with a brawl breaking out between United fans during the match. Former United boss Roy Keane said: “There were more protests – big problems at the club. “It’s a very bad start. Ten Haag needs time and money. There are huge problems upstairs.” Club icon Gary Neville added: “It was unacceptable to hand Ten Haag this team for the start of the season. Reality hit home. 4 Even Fred the Red could stand to watch at Old TraffordCredit: Getty 4 Ten Hag left Cristiano Ronaldo on the bench after the superstar requested a transferCredit: Reuters “The time has come for the Glazer family to sell the football team. “Manchester United is the easiest team to face in the league. For that first goal, Fred and Scott McTominay chase back. “How is it in this position? I was in complete disbelief. They tear like a knife through butter.” United legend Paul Scholes gushed: “For McTominay to run the ball forward when he has Jadon Sancho and Marcus Rashford in front of him is criminal.” Seagulls boss Graham Potter followed up a 4-0 win over United at the Amex in May to claim that historic win at Old Trafford. He hailed Welbeck who was doubtful for the game with a stomach bug. Potter said: “He would have stuck the toilet on his back to play, but it would have slowed him down. He was amazing.”