The Serb, seeded 10th, will play the victor of Saturday's second semi-final between Roger Federer and David Goffin.
Djokovic has reached the Western & Southern Open final five times...
Djokovic only needs this title to complete the set but he had to fight hard to overcome Cilic 6-4 3-6 6-3 on Saturday.
World number 17 Bertens, who played and won two matches on Friday after rain interruptions this week, looked fitter that two-time Wimbledon victor Kvitova in hot, humid conditions.
Still Barty fought back and had a break point in the final game that would have leveled the score at 5-5, but Halep sealed victory with a backhand victor.
"But it got better towards the end, I'm glad my serve has worked well all week".
The Canadian was staying in the match with his huge serve, topping 140 miles per hour on several occasions, and holding his own in the rallies, using a lethal backhand slice to trouble Djokovic.
"In the end, very few points, really, decided victor", said Djokovic.
Roger Federer 's match against Leonardo Mayer was postponed until Friday as well, along with several others pushed back by day-long rain that made a mess of the brackets.
"I had to keep it cool, she gets lot of balls back", Keys said.
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"I think also I'm less stressed", she said.
Cilic came into the contest having won their last two meetings, including victory in the Queen's final earlier this year, and also with the knowledge that he had a touch more pedigree at the venue.
Cilic controlled the second set, taking a 5-1 lead with two breaks before Djokovic momentarily came back into the set, but at 5-3 the Croat held to love to send the match into a decider.
"Yeah. Well, I must be very pleased with fighting spirit and staying mentally tough to overcome deficits in both matches", Djokovic said of his efforts after winning the quarterfinal match.
The match started with a low-key atmosphere after Wawrinka took the first set with a dominating performance in the tiebreak. I was clear with my game plan.
Milos Raonic would again break Djokovic's serve, this time to take a 2-1 lead early in the third set.
"Just a few points today decided it", added Djokovic, who saved nine of 12 break points and broke Cilic four times.
"It's tough to play against someone serving so big".
Cilic was to take on Pablo Carreno Busta, who like Raonic managed to book his quarter-final berth on Thursday.
Double Wimbledon victor Petra Kvitova reached the final four over Belgian Elise Mertens 7-5, 5-7, 6-3. "I'm really happy I can go through this, and tonight I'll have another match". She'll face Kiki Bertens, who advanced to her first Western & Southern final by wearing down No. 8 Petra Kvitova 3-6, 6-4, 6-2.