Southampton manager Ronald Koeman has said that a "very poor" first 20 minutes in their 3-1 loss to Manchester City proved costly.

Goals from Kevin de Bruyne and Fabian Delph gave City a two-goal advantage with less than a quarter of the game played and they conceded a third goal to Aleksandar Kolarov after Shane Long had grabbed a goal back.

After the final whistle, Koeman told BBC Sport that the Saints failed to take advantage at "key moments" in the match.

He said: "We had a bad start. If you make those kind of mistakes against City, you lose the game. We made them strong because we lost so many balls when building up from the back. You can't win if you play at that level.

"At least in the second half we played good football. We kept the ball much more than in the first 20 minutes. We had a big chance through Dusan Tadic to make it 2-2. These are key moments to get something out of the game.

"We had good ball possession and that has to be one of our strengths. But for the first 20 minutes, it was very poor."

The loss to Man City saw Southampton drop to ninth place in the Premier League table.