I think he was down a break in the second after being ahead with an early break, watching the livescore I obviously thought 'there we go...' but apparently it wasn't a good day to choke, there's always the final.
PHM had some difficulties to read Millman's serve in the first games. They were both winning easily their serve, though Millman more easily. PHM just couldn't return.
Then it was more even as far as the match progressed. There wasn't a lot of rallies. Millman isn't at all a claycourter. At the end of the first set, PHM raised a bit his level with a stunning FH to get 2 SPs. Millman saved them, but the third one was the good.
I think Paulo was overall a bit passive. He was of course the better player in the rallies, but he didn't attack a lot. It looked like he was waiting for Millman's errors (and they often came). His BH worked well, but I found him a bit slow (especially his defense isn't anymore what it used to be), and not aggressive enough with the FH.
I think he's a pretty good shot tomorrow against Zverev if he keeps as focused as today, and overall as consistent.