The fiery Italy international was involved in an unseemly post-match melee as Southampton slipped to a third consecutive defeat amid an injury crisis against Aston Villa on Wednesday, but he returned to St Mary's Stadium and grabbed the headlines for the right reasons.
A superb individual effort from the big-money close-season signing was the least Mauricio Pochettino's team deserved in a match they dominated for long periods after Sergio Aguero continued his purple patch in front of goal in the 10th minute.
Manuel Pellegrini's City won at West Brom on Wednesday, but this was a display far more in tune with the away-day woes that threaten to derail their Premier League title bid.
Midfielder Victor Wanyama suffered a hairline fracture to his leg and right-back Nathaniel Clyne damaged his pelvis in midweek, meaning Jack Cork and Calum Chambers came in as two of four changes in Pochettino's injury-ravaged side.
Samir Nasri teed-up Aleksandar Kolarov and the overlapping left-back's low cross was clinically dispatched first time by Aguero for a 17th goal in 15 matches.
Kolarov glanced wide from a Nasri corner three minutes later and Aguero blazed Pablo Zabaleta's 31st-minute cut-back over, but they were rare moments of encouragement for City.
Adam Lallana was involved in much of Southampton's best work but could not bring down Chambers' lofted pass in time to avoid Milner's last-ditch clearance.
Osvaldo superbly brought down Davis' long pass and turned Vincent Kompany inside out to arch a shot into the top-far corner via the crossbar.
But City's Argentinean talisman was restricted to half chances thereafter and they could be eight points behind Arsenal when the leaders arrive at the Etihad Stadium next Saturday.
