McShane praised Mauricio Pochettino's side after Saturday's match, although felt City did not do themselves justice.
"It was very disappointing," he said. "We have been doing well recently and I think the first 45 minutes killed us, really.
"We never really got going and they were bang at it, so three goals in the first half has killed us. It is disappointing.
"Southampton were very good, a very good side and have done well this season, but I just think we didn't get going in the first half.
"In the second half we played better but we were 3-0 down, so the game was basically nearly over.
"They are a good side, all credit to them, but I think we just made it easy for them in the first half."
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