Playing at the near packed Center Court here, Novak Djokovic stormed into the Cincinnati Open final for the sixth time by overcoming big-serving 2016 tournament champion and seventh seed Marin Cilic of Croatia 6-4, 3-6, 6-3 in semi-final match.
Argentina's world number three del Potro had played just six points in the first game of his postponed second-round match against Chung Hyeon before the rain came again.
Djokovic only secured his defeat of Cilic late in the final set, breaking for 5-3 and finishing off the hard-fought victory in the next game.
Djokovic has lost all five of his Cincinnati finals.
With both players near their consistent best, Wawrinka saved two break points in the sixth game, while Federer offered his compatriot none.
It was the ninth win without a loss for Djokovic in the series with the Canadian. She beat the Australian in the semi-finals in Montreal an her way to the title there.
The Serb, a 13-time Grand Slam victor, claimed a memorable Wimbledon title in July - a victory that marked the culmination of a two-year rise and fall from the very top of the game. Djokovic leads in head-to-head title matches 11-6.
"I feel like I'm trying to defend my title from way back when", he said.
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Halep is seeking her first Cincinnati championship after losing in the finals previous year and 2015.
Djokovic, a five-time finalist in Cincinnati, is aiming to lift the trophy at the sole Masters 1,000 series event he has never won. The 10th-seeded Serb squared the match as the day's second bout of major rain moved in.
Former champion Cilic made his way to the semi-finals with a 7-6 (5) 3-6 6-4 third-round win over Russia's Karen Khachanov before toppling Spaniard Pablo Carreno Busta 7-6 (7) 6-4.
"I never felt, so to say, embarrassed to say that I'm someone who makes mistakes, and I'm not proud when I break the racquet, especially I know there are kids around and watching, and I'm not proud of it, but sometimes it's just - it's too strong, and you let it out", he said.
Because of the tournament's many weather delays, Halep will be back on the court later on Friday to play Ukrainian Lesia Tsurenko in the quarter-finals.
The 20-time major victor earned himself three break points in game two with the assistance of a magnificent cross-court forehand pass, but he failed to use any of them to his advantage. "To see where I was also few weeks ago, I'm really happy to be here", he added.
She will face rising 20-year-old Aryna Sabalenka of Belarus, who upset Madison Keys of the United States 6-3 6-4.