The general consensus here is that anybody who wins the World Tour Finals falls off a cliff. Tsitsipas isn't proving that theory wrong. He's been patchy and slightly off all year.Thiem played a great 3rd set. Some clean hitting and great serving.
Tsitsipas on the other hand, not good enough. He was playing at a much higher level last year. His movement looks quite bad and returning is probably the worst in the top 10. Needs to introspect.