The Germany international made his first Premier League debut at the Emirates Stadium for the visit of the Saints alongside French defender Laurent Koscielny.
Mustafi signed a five-year deal with the north London side last month after Arsenal agreed a reported £35m transfer fee with La Liga side Valencia.
The Gunners fell behind due to Petr Cech’s first-half own goal before Mustafi’s centre-half partner Koscielny levelled with a brilliant overhead kick.
And Santi Cazorla netted an added-time winner from the penalty spot after Southampton captain Jose Fonte was adjudged to have fouled Olivier Giroud.
Former Arsenal midfielder Parlour expressed his reservations over Mustafi’s debut performance for the north London outfit at the Emirates Stadium.
“It was a little bit 50-50. It was the first time that i have seen him live. He made a couple of bad mistakes. But he also looked like a real leader. that’s what they’ve missed,” Parlour told Goals on Sunday on Sky Sports.
Arsenal finished in second place in the Premier League table last season and 10 points behind champions Leicester City.
Wenger signed five players in the summer transfer window as the Arsenal manager addressed some weaknesses in his squad.
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