However, Guardiola remains wary after Ole Gunnar Solskjaer’s men recovered from losing 2-0 at home to Paris Saint-Germain in last season’s Champions League last 16 to progress.
“It’s a good result, but it is not over because it is United,” Guardiola told Sky Sports.
“Last season is a good example against PSG. Hopefully in front of our fans we can make a good game and reach the final.”
United have shown their ability to win at the Etihad already this season as they tore City apart on the counter-attack to shock the Premier League champions on home soil just a month ago.
But City restored their recent dominance of this fixture with a third consecutive win at Old Trafford and a fourth in five away derbies since Guardiola took charge.
The Catalan responded to the problems United posed his side last time out by deploying an extra midfielder with both City strikers Sergio Aguero and Gabriel Jesus left on the bench.
Guardiola’s tactical plan worked to perfection as a fluid front four of Silva, Mahrez, Raheem Sterling and Kevin De Bruyne were too fleet of foot and thought for a United defence without the injured Harry Maguire.
“I enjoyed it a lot, especially because it worked,” said Silva. “I think the first half was the perfect 45 minutes, we could even have gone to half-time winning four or five because we missed a few chances.”
‘Did not cope’
The Portuguese international was back to his best and opened the floodgates by smashing a shot into the top corner from outside the box on 17 minutes.
Silva turned creator for City’s second as one pass split the United defence and Mahrez rounded David de Gea to slot into an empty net.
Five minutes later it was 3-0 as De Bruyne left Phil Jones flat on the ground before his powerful shot was parried by De Gea into the path of the unfortunate Pereira, who could only turn the ball into his own goal.
“After they scored we did not cope with that setback well enough,” admitted Solskjaer.
Only a brilliant save from De Gea to deny Silva a second and Sterling’s miss from a inviting Kyle Walker cross prevented the scoreline from becoming even more embarrassing for United before the break.
“We just did not recover from those goals until half-time when we could get into their heads a little bit and we did better second half,” added Solskjaer.
City eased up after the break and United grabbed a lifeline when they finally caught the visitors cold on the break as Mason Greenwood teed up Rashford to calmly slot into the far corner for his 17th goal of the season.
There was no late rally from the Red Devils to further cut City’s advantage, leaving Solskjaer hoping for a repeat of the miracle in Paris that landed him the United job on a permanent basis last March.
“We’ve shown before we’ve been down from a home tie and turned it round,” said the Norwegian.
“We’ve just got to believe when we go to the Etihad and put a performance on.”