The 12th-seeded Dane produced a resilient display to beat former Wimbledon finalist Berrettini 4-6 6-4 6-3 in just over two hours.
In a match that had originally been scheduled for Saturday but was delayed by persistent rain at the Qizhong Forest Sports City Arena, Berrettini broke for a 5-4 lead in the first set before calmly closing it out.
Berrettini appeared to be on the brink of closing out of the match as he continued to ease through his service games, but Rune raised his level to strike in the 12th and final game of the set and level the match.
The decider ultimately came down to two epic games, with Rune saving a break point on his way to holding serve for 1-0, before taking his third break point opportunity of the eighth game to claim the advantage.
“It felt like he didn’t do many things wrong in the first set.
I made a few errors, but then he was just on me.
He didn’t allow me to make many mistakes.
I think the same happened in the second and third sets, just the other way around.
Every time he got slightly central or short, I was there to punish his shots.
“It was a good match, honestly. I think the tennis was very high quality.
We were hitting a lot of winners, good serves, good movement, so I’m very happy to start my tournament like this.
