Harry Kane was seen by many as the man who would make sure Manchester City stayed in the premier league. He may have blown the title race wide open six months later.
The side that tried so hard to sign him at the start of the season was sunk by his performance on Saturday night.
Kane would have been performing more frequently at the stadium if Daniel Levy hadn't been unwilling to negotiate with City.
He showed why he was City's top centre-forward target, and why Levy refused to budge on his asking price, when he put on a performance that showed exactly why he was made his top centre-forward target.
Alan Shearer described Kane's performance on Match of the Day as one of the best all-round centre-forward performances he had seen all season.
He was too good for City's centre-halves Aymeric Laporte and Ruben Dias, and it is not very often that we say that. He was too smart for them.
Whatever was asked of Kane against the defending champions and league leaders, the current England captain delivered - from his exceptional link-up play to his ruthlessness in front of goal.
Kane started and finished the move that gave Spurs a 2-1 lead.
It took a brilliant Ederson save and a VAR decision to stop him from extending his side's advantage in normal time but, after City looked like they had rescued a point with a last-ditch Riyad Mahrez penalty, it seemed fitting that Kane would have the final word.
He did that with a winner in the final seconds of the game.
Kane was able to continue his celebrations after the game with the travelling Spurs fans, who sang "Harry Kane, he's one of our own" at the final whistle.
During the Spurs home win over City on the opening weekend of the season, the Spurs supporters had a different chant about their skipper.
They chanted "Are you watching, Harry Kane?" with the 28-year-old absent after asking to leave the club and seemingly on the verge of a big-money move to the opposition.
There was no need to ask where he was this time. Kane was doing a lot more than just watching.
Shearer explained that part of the gameplan was to keep finding Kane with short passes, because no City defenders wanted to drop in with him.
Spurs kept getting runners forward to feed off Kane and get in behind. His pass to Son Heung-min for their first goal was absolutely amazing.
As soon as Ryan Sessegnon picked up the ball, I knew that Kane was going to score because no-one was going to pick him up. The clinical finish came after that.
It was amazing to watch. He did everything well, including his winner. Say what you want about the defending, and it was rubbish, there was only ever going to be one guy getting on the end of that cross and it wasn't Kyle Walker.
Spurs were able to take advantage of Kane's brilliance by ending City's 15-game run in the league and then reverting to their poor form to shock the league.
Kane's display was something of a surprise, because this has not been a vintage campaign for him, in terms of goals. He had only scored five times all season before facing City.
This was a timely reminder of his class, and his manager and boss would have enjoyed it.
The way in which City operate with a defensive high line meant that the Italian's preferred approach of sitting deep and flying out on swift counter-attacks always had a chance.
Having a world-class player who had a very good day helped, but Kane was not the only reason it worked so well.
It was painful for City fans, but they won't face a perfect performance like that every week.
It would be wrong to say that this defeat is a crisis for the team.
It opens the door for a dangerous-looking side who are on an eight-game winning run in the league and gathering confidence and belief.
City can ill afford another slip-up when they travel to Merseyside to take onEverton next weekend, as the Reds could reduce their lead to three points on Wednesday when they play their game in hand.