Manchester United manager Jose Mourinho has claimed that his players were left feeling tired against Southampton due to the hot conditions at St Mary's Stadium.

The temperature hit 19°C on the south coast as the Red Devils battled to a narrow 1-0 win, keeping them joint-top of the Premier League table alongside Manchester City.

United were left holding on at one point in the second half, with Mourinho confessing after the game that his side struggled in terms of fitness due to the hotter-than-anticipated conditions for the late-September clash.

"I think they were really tired at the end," he told reporters. "Nine of them didn't play in midweek, so nine of them it's not even an accumulation of fatigue. I think the weather was beautiful.

"Even if you train at 11am, 12pm, 3pm in Manchester, we don't get this weather. Seriously. The last time we had this was in Los Angeles [for preseason] and then in Macedonia [for the Uefa Super Cup], and I think they felt it.

"I saw some players not sharp. Great spirit and always trying, but not the same sharpness. So if your opponent is coming with everything against you, let's do it for 10 or 15 minutes and stay solid."

Mourinho, who was sent off towards the end of the match, takes his side to Russia for their next outing as they face CSKA Moscow in the Champions League on Wednesday night.