Bautista Agut, 30, had lost his past three meetings with Berdych, the 33-year-old former world number four who has slipped to 71 in the rankings.
The first came in October 2016 in Shanghai.
Bautista Agut took their match in straight sets, going 6-4 6-4 over Stan the Man.
Arsenal midfielder Aaron Ramsey yet to sign Juventus pre-contract agreement?
Ramsey joined Arsenal from Cardiff in 2008 and has won the FA Cup on three occasions - scoring the decisive goal in two finals. Ramsey has made 14 starts and 11 substitute appearances in all competitions this season.
The second began as an even affair with a string of impressive baseline rallies that Djokovic initially dominated, his athleticism and power forcing more errors from his opponent. The Serbian has been nearly unbeatable on hard courts over the last six months, but Bautista-Agut trumped him in a tactical masterclass.
Things quickly turned in Bautista Agut's favour, though, as his punishing groundstrokes penetrated Djokovic's previously solid defence.
It could not halt Bautista Agut, however, and after edging the breaker, he broke his rival in the opening game of the decider - an effort that proved crucial as he held firm to record only his second win over the US Open champion.
I just think he dropped his level a little bit and I managed to get on top of him. That's it, ' a frustrated Djokovic said in his post-match press conference.
Samsung reportedly working on Galaxy A50 and Galaxy M20 smartphones
The report also affirms that the A50 will be powered by Samsung's Exynos 7 9610 chipset with four Cortex-A73 cores and four A53s. Although we fully expect it to be launched in the first half of 2019 , picking out a particular month will be tough right now.
"He played really well, smart, changing up the rhythm and the pace of the ball and moving me around.I was kind of in a corner and I had to find my way and fight my way through".
The Italian player took advantage of Guido Pella's retirement on Wednesday, Cecchinato is coming from the best season in his career.
"I will remember this match for [the rest] of my life", he said after the match.
"This is what I was looking forward to, to get from this tournament, as many matches as possible, to get ready for the Australian Open, so I'm very pleased".
Here's how Meghan Markle's parents spent Christmas in the USA
They may be part of the Royal Family but even Prince George and Princess Charlotte have their parents up at the crack of dawn on Christmas morning.
In the other semifinal, Tomas Berdych, a victor over Pierre-Hugues Herbert, continues his comeback against French Open semifinalist and No. 4 seed Marco Cecchinato.