Defender champions Manchester City slid into the quarter-finals of the Carabao Cup in the wake of seeing off a Southampton side who were centered around harm restriction after their embarrassing home defeat against Leicester.
The Argentinian effectively put the game to bed soon after the break with an opportunistic finish, but Jack Stephens’ 75th-minute header was just rewarded for a spirited second-half display from Saints.
Fresh from their 9-0 home drubbing at the hands of Leicester City in the Premier League, though, Ralph Hasenhuttl’s side is now winless in five in all competitions.
Then Bernardo Silva received a short corner, floated a ball into the mixer from the edge of the box and Otamendi rose highest to head past Alex McCarthy from six yards.
Seven minutes before the break, after more relentless pressure from City, Aguero made it 2-0.
It was a trademark City goal as they strung together slick pass after slick pass before the 31-year-old side-footed home Kyle Walker’s inch-perfect delivery from the right.
The problem for Saints was City were winning comfortably having barely got out of second gear.
The hosts looked as though they could score at will, and all it took for Pep Guardiola’s side to go 3-0 ahead was for Silva to slightly up the tempo.
In the 56th minute, he burst past two defenders after cutting in from the right, laid the ball off to Riyad Mahrez, whose deflected shot was turned home by Aguero from close range after the Southampton defense couldn’t respond quickly enough.