Head to heads are 2-2. Their last match was in May 2015. Thiem won on clay in straight sets. Both Simon’s wins ( on hard and clay) went to 3 sets.
Thiem didn’t face a single break point against Muller. He only managed to break once himself. Simon started slowly against Jaziri and was broken at the start. He fought back to take the set in a tie break and then Jaziri ran out of steam.
I think this will be tight but Thiem has looked so solid this week and has not faced a single break point.
Wait for 1.80 on Thiem. We have a fair chance of 3 sets if Simon can stay focused.