Manchester United boss Ole Gunnar Solskjaer saw his side end Manchester City's 28-game unbeaten run on Sunday, but the win was no fluke result.
The Red Devils put in a brilliant performance at the Etihad to halt the Premier League champions-elect in their tracks.
Solskjaer has often faced criticism of his managerial ability, with many feeling he isn't a strong enough tactician.
But with just one half-time tweak to his side's system, he dispelled those suggestions.
The Norwegian boss saw his side take an early lead through a Bruno Fernandes' penalty in the first minute, before sitting back and letting City dominate possession.
However, shortly after the re-start, Solskjaer changed his side's tactical style and pushed the team forward in search of a quick second.
The change worked, as Luke Shaw drove forward with the ball and played a one-two with Marcus Rashford before drilling into the bottom corner.
Solskjaer discussed the change after the match, and explained that taking an early lead set the tone for the rest of the game - something he wanted to replicate in the second.
He also claimed that his side stayed too rigid in their shape after taking the lead, because they were simply playing to avoid defeat.
"Every game lives its own life this season, it’s unpredictable, it can go up and down, that’s just human nature," said Solskjaer.
"Today, we started really brightly on the front foot.
"When you get the 1-0 lead it sets a tone for the game. I thought we were excellent in the first 10 or 15 minutes, then settled into our shape, because we played too much on the result.
"We adjusted that at half time to be more positive again and the second goal was incredible.
"We’ve got to do everything we can to keep the performance levels up, of course."
