Man United's Louis van Gaal defends Angel Di Maria, praises Adnan Januzaj

Louis van Gaal insists Angel Di Maria needs more time to adapt to the Premier League despite substituting the British record signing at half-time during Manchester United's 2-0 win over Sunderland.

Di Maria, 27, endured a difficult opening 45 minutes at Old Trafford on Saturday before being replaced for Adnan Januzaj at the interval, who played a part in Wayne Rooney's second goal of the game.

The Argentine has struggled to recapture the form he showed at Real Madrid since signing for United for 59.7 million pounds last summer, and Van Gaal believes replacing the midfielder was the right choice.

"We have to give Angel more time to adapt to the Premier League; it's not so easy with the high tempo," he told the club's official website. "I want to give him time, it's also not easy to change a player of his quality, but I have to make these decisions."

Van Gaal praised Di Maria's replacement Januzaj, who saw his shot parried into the path of Rooney by Sunderland goalkeeper Costel Pantilimon late on to ensure the three points.

"I was very happy that he registered an assist for the first time, it's something I like to see from every player," he said.

Ashley Young also had positive words for the young Belgian, adding: "He was terrific. As a winger, you want to get the ball and run at your full-back. He did exactly that, did exactly what the manager asked him to do at half-time.

"It was a great performance by him but it was a team performance and everyone in the team, everyone that came on, was fantastic."

United struggled to create chances in the first half with the home supporters shouting "Attack, attack, attack" in an effort to inspire their players, and Van Gaal admitted his side were not good enough in the opening 45 minutes.

"We started the match poorly," he said. "I think we were nervous, which is understandable after the defeat to Swansea. After the first quarter of the match, we started to create more chances and we played much better in the second half.

"We had much more composure on the ball, the tempo was better and we stretched the play from one wing to another. I was pleased with the performance, especially in the second half, we scored twice but could have got more."

The breakthrough came when Radamel Falcao was brought down in the Sunderland area in the 65th minute for a penalty -- which Rooney dispatched -- although referee Roger East sent off Wes Brown despite John O'Shea appearing to foul the Colombian striker.

"It was comfortable [in the second half] because they had 10 men and we didn't give them any chances in the second half," he continued. "We played with control; it's a step in the process to finish a game off when you are winning.

"Perhaps [Marouane] Fellaini could have scored, and there was also [Antonio] Valencia's shot, so we could have scored more goals. Goal difference can be very important at the end of the season in this rat race for the top four."

Rooney scored a brace to set a record as the only play to score 10 or more goals in 11 consecutive Premier League seasons, with Van Gaal saying: "He said to me, and he was right, that he usually hits penalties high into the goal. Today, he shot along the ground because of their tall goalkeeper and I was very happy that was the case."

On the club's recent injuries, the Dutch coach added: "Luke Shaw [had a tight hamstring] and [Phil] Jones was ill. I cannot put those players in my line-up. Victor Valdes also has a problem and wasn't on the bench. I had to make three changes during our final day of preparation."