Saints started sluggishly in south London, and could well have fallen behind only for Lions forward Magaye Gueye to spur a gilt-edged chance after latching onto goalkeeper David Forde’s long punt forward.
Koeman’s charges improved considerably after the break, and went on to record a comfortable win over their Championship opponents thanks to goals from Jack Cork and Graziano Pellè.
“I’m happy about the reaction in the second half – we were much better and we had many chances,” Koeman told youtube.com/southamptonfc
after the game.
“The first half was very bad. It looked like the team was playing at 70% and you know that in cup football you have to be at 100% – if not, you get into trouble.
“We were in trouble in the first half, and maybe the best example of that was the chance they created from the long ball by the goalkeeper to put the striker one-against-one with Forster. That’s impermissable at this level.
We spoke at half time, and I was very unhappy. You can play badly – it’s part of the job – but you have to give 100%. They (Millwall) gave more than us, and you can’t accept that.
“I had to change the system at half-time, and the second half was much better.”
Koeman was particularly pleased for forward Pellè, who scored his first goal for the club in the closing stages.
“That’s a great feeling for a striker,” said the coach.
“Of course, they are happy if the team is winning but if they don’t score for two or three matches in a row then they get a bit nervous.
“Maybe this will give him the feeling and the confidence that he is a good striker.”