Then he watched Roger Federer advance to the finals as well when David Goffin retired in the second set with a shoulder injury.
"But it got better towards the end, I'm glad my serve has worked well all week".
"It's going to be a big challenge for me to play another final and win it", she said. "I used my forehand and serve well today".
Only a couple of hours later, Djokovic stopped Milos Raonic 7-5 4-6 6-3, improving his career record to a ideal 9-0 against the Canadian.
"Hopefully I can get it done this time", Djokovic said.
But the weather cleared long enough for del Potro to polish off a 6-2, 6-3 win over the South Korean to set up a meeting with Australian Nick Kyrgios for a place in the quarter-finals - a match originally set for Thursday night but now on tap for Friday.More news: Turnbull 'holds crisis meeting' amid calls for Dutton to challenge leadership
Djokovic beat 2016 victor Marin Cilic 6-4, 3-6, 6-3 to earn his place. "I've now got a hard final against a tough opponent".
"That's not how I wanted to win, but I'll take it", the Swiss said.
Djokovic has lost all five of his Cincinnati finals.
Djokovic, outside the top eight seeds for the first time since 2006, opened his campaign with a 6-4 7-6 win over Steve Johnson, in which he squandered his first eight match points.
He had to work for more than two and a half hours to overcome Cilic, the 2016 champion in the combined WTA and ATP event.
However, Djokovic broke back in the eighth game before serving out clinically to secure victory.More news: Winx beats Black Caviar's record with 26th straight win
"I just need to get out there and really fight, I was telling myself to fight", the two-time Wimbledon champion said.
Djokovic leads in head-to-head title matches 11-6 and the overall series 23-22.
On Sunday she'll try again against Dutch outsider Kiki Bertens, who will be playing her third final of the season after wearing down a tiring Petra Kvitova 3-6, 6-4, 6-2. About her opponent Halep said: 'She did great in French Open last year or two years ago. She became the first unseeded player to win in Cincinnati since Vera Zvonareva in 2006.
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. She's fighting all the time, all the matches, so she deserves to be there'.
Known as more of a clay-court player, Bertens has reached a hard-court final for the first time, spending more time getting accustomed to the different style of play.
Sabalenka, the 20-year-old number 34 who is still seeking a first career title, dropped the opening set on back-to-back double-faults.More news: Germany reaches deal on sending back migrants to Greece
After dropping the second set, Djokovic broke to go 3-1 up in the decider before complaining to the chair umpire about music that was audible from outside centre court.