Tottenham's Dele Alli was hit in the back of the head with what appeared to be a plastic bottle during his side's 2-0 win over Arsenal in the Carabao Cup quarterfinals at the Emirates Stadium on Wednesday.
The midfielder helped put his team ahead with a superb pass for scorer Son Heung-Min in the first half, then netted a beautiful goal of his own just short of the hour mark, running in and calmly chipping the ball over Arsenal keeper Petr Cech.
Minutes later Alli was hit in the head with something as Arsenal were about to take a throw in. The player did not appear hurt, and turned to the crowd and used his hands to gesture the 2-0 scoreline to them.
"It made the goal a little bit sweeter," he told Sky Sports.
Tottenham manager Mauricio Pochettino said he expected Arsenal to deal with the offending fan.
"Luckily, it wasn't a big issue," he told reporters. "When we play the derby we hate each other, in a good way, but that was in a bad way when you want to damage someone.
"I can't talk in general because I respect Arsenal fans, but one person made a stupid mistake. But I expect Arsenal take some responsibility and through the cameras can identify [who it was].
"It wasn't a problem but could have been a big issue."
A Tottenham fan was fined and banned for throwing a banana skin towards Arsenal's Pierre-Emerick Aubameyang when the sides met in the Premier League just over two weeks ago.
Both managers started strong XIs -- Son leading the Tottenham line with Harry Kane on the bench -- in a rematch of a Dec. 2 Premier League match which Arsenal fought back to win 4-2.
The in-form Son repaid his manager's trust on 20 minutes and Moussa Sissoko should have made it 2-0 minutes later on another counter, but he fired over the crossbar after breaking free on goal from a Christian Eriksen assist.
"It's a big derby, last time we were here we didn't have a great result and this is a special night," Son said.
Arsenal almost had a deserved equaliser before half-time, but Aaron Ramsey's first-time volley from an Alex Iwobi cross was somehow palmed off the post by Spurs backup keeper Paulo Gazzaniga.
The end-to-end action continued in the second half and Alli would double the visitors lead with a cheeky finish over Cech after being picked out by Kane, who'd only just come on as a substitute.
Arsenal were left to rue several wasted opportunities with Henrikh Mkhitaryan guilty in the first half, while the hosts also struck the woodwork on a couple of occasions.
Prior to the victory for Pochettino's team, Spurs had won only two of their previous 30 matches at the Emirates and Arsenal's former ground Highbury.
"A very difficult draw, another London derby. We have already played Watford, West Ham and Arsenal," Pochettino said, when learning they will play Chelsea in the semis.
"We shall see, Chelsea are a great team but we are excited. To be in the semi-final is fantastic for us."
Tottenham are looking to win their first silverware under manager Pochettino and their first since 2008 when they lifted the League Cup by beating Chelsea in the final.
Information from Reuters was used in this story.