MANCHESTER (AFP) - Arsenal manager Arsene Wenger said Danny Welbeck had been motivated by a desire to prove Manchester United wrong after he knocked his former club out of the FA Cup.

A Manchester-born United academy graduate, the England striker left for Arsenal last September after falling out of favour under new manager Louis van Gaal.

The Dutchman claimed Welbeck was not good enough to hold down a starting place at Old Trafford but his words returned to haunt him as the 24-year-old earned holders Arsenal a 2-1 win on Monday that set up a semi-final with Reading or Bradford City.

"We want all to do well when we play against our former club to show that we are a great player but it's not easy to deal with the mental situation of it," said Wenger, whose side had not won at United since September 2006.

"But he focused just on his game and didn't do anything special, just played football like you want him to play. I think he has shown mental strength because it's not always easy to deal with that."

Wenger added: "He wants to win. He is a team player. What I like with Danny is he's intelligent, he wants to do well for the team, he's a great talent and recently has done extremely well for the national team."

Welbeck's 61st-minute goal saw him seize on a back-pass from Antonio Valencia before rounding David de Gea to score, and he celebrated by clenching his fists in an apparent show of vindication.

United now have only Champions League qualification to aim for, with Arsenal one of the teams competing with them for a top-four finish in the Premier League.

Wenger said his side's victory would give them extra belief.

"Every win makes you stronger," he said. "We have won at Man City and that helped us to deal with another big game.

"And when you can win big games, it's more mental. We know we have the football level but the belief is important."