Chelsea manager Guus Hiddink was disappointed after his side failed to convert possession in chances during Saturday's defeat at Swansea City.
The Blues suffered their first league defeat since the Dutchman took over as interim manager.
They keep their 10th position in the table and will face Manchester City at Stamford Bridge next week.
"We expected a difficult game here of course," Hiddink told reporters.
"They needed three points theoretically, whereas we were safe already. We had already achieved a rather soft target. We expected a lot of opposition.
"In the first 20 minutes we created some half-chances, but we were sloppy in materialising those options, thinking maybe it would come later. No. If you don't materialise those, there is a law in football everyone knows which is that you can get in trouble, which we did not long after, going 1-0 down.
"In the second half we played most of the time in one half but we weren't able to create a lot of chances.
"The idea behind it [resting Thibaut Courtois] was that [Asmir] Begovic, being a good goalie, which he has proven already in many Premier League games, is doing his job as a professional very well in training to keep himself in shape," Hiddink explained.
"Every training session he is 100 per cent committed and on top of that he is helping out Thibaut Courtois in a very good professional way, and that's why I rewarded him by having him play at least once.
"[Why Matt Miazga was replaced by Kenedy?] We had had some half-chances which we were not sharp enough to materialise.
"We went 1-0 down with some sloppy defensive work and on top of that he had a yellow card, and I didn't want to take the risk of him getting a second yellow.
"That was the main reason to make the substitution."