Dortmund's German midfielder Mahmoud Dahoud (left) and Tottenham Hotspur's English midfielder Harry Winks compete for the ball at Wembley Stadium in London on Wednesday. Photo: VCG

Tottenham Hotspur still have work to do to reach the next round of the Champions League despite a convincing 3-0 victory over Borussia Dortmund in their last-16 first leg on Wednesday, said coach Mauricio Pochettino.

Tottenham stunned the Germans with a goal two minutes after halftime from Korean forward Son Heung-min and struck twice late in the game through Belgian defender Jan Vertonghen, who was deployed in an unusual left wingback role, and substitute Fernando Llorente.

"It is a massive, massive performance and effort from my players," Pochettino told reporters.

"My players are heroes. They deserve a lot of praise because their effort this season is amazing.

"It is only the first half of the tie - 3-0 is a very good result, but we must go to Dortmund with the idea of winning. It is a very good result but there is a lot of work to do."

The second leg is in Germany on March 5.

Tottenham were on the backfoot in the first half against the Bundesliga leaders, who had conceded only two goals in the entire group stage and had the better scoring chances.

The Argentine coach said he had to talk to his players at halftime to discuss ways of slowing their opponents down, with Dortmund's Jadon Sancho wreaking havoc down the wing.

"I would not say the team were nervous but the second half was much better. At halftime we showed them a few situations that could have been different," Pochettino said.

"We tried to help the team make the right decisions and perform in the best way. You need some luck, too. For me it is only the first leg, the first half but it is a very good result."

The result equalled Dortmund's heaviest away defeat in the Champions League.

The Germans also suffered a morale-sapping 3-3 draw against Hoffenheim last week in the Bundesliga after leading 3-0 and were also eliminated from the German Cup by Werder Bremen on penalties.

"We played well in the first half, had a couple of chances, We defended really well and played well going forward," Dortmund coach Lucien Favre said.

"In the start of the second half we gave it away. It was a gift. After that we tried to play a bit too hastily and it was very, very difficult for us. After the second goal it was harder to hold on to the ball and create chances."

For Favre and his players it is now back to the drawing board.

"There are periods of a season when things aren't top, top, top. It is what it is. We need to analyse and work hard to avoid and correct these errors," he added.