The 37-year-old top seed was more like his old self on Friday, defeating eighth seed Kei Nishikori in two high-quality sets.
In the last 12 months on hard court, Djokovic has held serve 2.0% more, doing so 87.5% to 85.5%, and broken opponents 3.5% more, too, with a 29.4% break opponent figure, compared to Zverev's 25.9%, and this data does give him a solid edge for tomorrow.
There was a subtle shake of the head when Federer similarly lost his serve at the start of the second set.
"It was the same length, actually, as all three of my matches went the same length basically, an hour and 52 (minutes)", Federer said.
"I'm happy how the body has felt this week".
"Serving, I think, it's okay, could be even a little bit better. He is a quick leaner and an intelligent human being and I think the composure he is now showing [is proof] that he is ready to take his tennis to another level".
Djokovic is targeting his 72nd career title here on Sunday.
Coric described Djokovic as a close friend.
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"It was one of the best matches of my life", said Coric, who had nearly skipped the tournament due to neck pain.
The 31-year-old Serb will also overtake Federer for the No.2 spot in the ATP rankings after claiming a 17th consecutive win in his 1000th senior contest.
Djokovic will be up a place to second in the world - overtaking 20-time Grand Slam champion Federer - when the rankings are released on Monday.
Djokovic, who has won the last two Grand Slams, at Wimbledon and the U.S. Open, is now world number three, but could move up a spot if he books a place in Sunday's final.
"I wasn't - I feel like - playing as well as I'm playing today", he warned.
"I felt like I got some great rhythm, whereas in Cincinnati I came out of the tournament, I was, like, "I don't know where my game is".
After falling 3-1 down, the German angrily smashed his racquet - earning a code violation - before throwing it into the crowd.
'When you are winning like this obviously you are calm when you are losing things are a bit different, ' Djokovic, himself, said after dispatching Zverev.