Guardiola’s side were labouring to break down United until Aguero came off the bench to end their stubborn resistence at Bramall Lane.
City striker Gabriel Jesus had a penalty saved by Dean Henderson in the first half but with 17 minutes left Aguero bagged his seventh goal in four appearances in 2020.
His 21st goal of the season in all competitions moved second-placed City to within 13 points of runaway Premier League leaders Liverpool, who have two games in hand on the champions.
While City’s hopes of winning a third successive title have been shattered by a combination of their own failings and Liverpool’s incredible form, there is still much to play for this term.
Guardiola harbours dreams of leading City to their first Champions League crown and they also face an FA Cup date with Fulham this weekend, followed by the League Cup semi-final second leg against Manchester United.
With those cup ambitions in mind, Guardiola will have been encouraged by the way City coped with the Blades’ aggressive game-plan and emerged with a fourth win from their last five league matches.
“Sergio is on fire right now. Strikers need momentum. It’s good for us to have strikers in this form,” Guardiola said.
“I’m so happy with the team. I know what it’s like to play here, it is a tough place. We controlled it well and in the end we created chances to win.”
Keeping just their third clean sheet in 14 league games was another boost for Guardiola, who gave French defender Laporte his first appearance since August after recovering from a serious knee injury.
Laporte had been back in training for over a week, but his presence in the starting line-up for the first time in 143 days was a surprise as Guardiola had hinted he was not set to feature just yet.
“We knew that Aymeric couldn’t play for 90 minutes, that’s why we played five at the back to protect him a little bit. He’s a crucial player for us, we’ve missed him, it’s good for us to have him back,” Guardiola said after Laporte came off in the closing stages.
Guardiola might have been regretting his gamble when Muhamed Besic crashed into Laporte’s ankle with an ugly tackle that earned a yellow card.
– Crucial contribution –
City’s first half pressure should have yielded the opening goal in the 35th minute after Riyad Mahrez superbly prised open United’s defence.
Sprinting down the right flank, Mahrez cut into the area and evaded two defenders with some nimble footwork before Chris Basham’s trip sent him sprawling.
With Jesus replacing Aguero in starting line-up, it was the Brazilian who took the penalty, but his effort was superbly pushed away by Henderson.
City felt Henderson moved off his line before Jesus made it three misses from his last six penalties, but their appeals for a retake were ignored.
City were not on peak form but even at less than full power they were still dangerous and Henderson had to keep out Jesus’s close-range header.
Guardiola sent on Aguero for Jesus and within six minutes the switch paid off as City finally broke through in the 73rd minute.
Kevin De Bruyne wriggled into space for a perfectly-weighted pass that picked out Aguero’s run to the far post, where the Argentine had the simple task of slotting home.
De Bruyne’s crucial contribution made him the first player in Premier League history to provide 15 or more assists in three different campaigns.
