Garry Monk has admitted that Swansea City were made to pay for 'continuous mistakes' as a "horrible" first-half display saw them thrashed 5-0 by Chelsea.
Oscar opened the scoring inside a minute at the Liberty Stadium on Saturday and the Blues took advantage of some defensive errors to go four up by the interval.
The Welsh outfit slowed down their "devastating" visitors as only Andre Schurrle added to the scores after the break, but that was not enough of an improvement for Monk to forget an opening 45 minutes which he ranks as Swansea's worst performance this season.
"It was a horrible performance first half - way off our standard," he told the club's official website. "We made mistakes continuously against a team like Chelsea, who punished us heavily. And credit to them, their performance was devastating to take advantage of our mistakes.
"They were 4-0 up at half time, then it was always going to be an uphill battle. We had to be perfect to stand a chance, and we were far from perfect. Everything we worked on, we didn't do. It's disappointing. We were marginally better in the second half, without any real chances. But the first half was the worst of our season. We didn't do ourselves justice at all.
"But we've shown in the past we can react straight away. We have very good players. The big picture this season is that we've done very well, which is what makes performances like today harder to watch. We will learn from this."
Diego Costa bagged a 15-minute double before Oscar completed his own brace as Chelsea ran riot before the half-time whistle.
