Clijsters also overcame three match points on the way to her 2-6, 7-6 (4), 6-2 victory Sunday in the $2 million Cincinnati Womens' Open. The delay happened late in the second set, shortly after Sharapova failed to close out Clijsters for the third time.
"When the rain started falling, I was like, 'Oh, no,'" Clijsters said. "I was feeling like I could hold here and get a chance for a break. I didn't feel like I was really in trouble. Before the break, I thought the match could go either way."
Clijsters, the defending U.S. Open champion and world's seventh-ranked player, bounced back from connecting on only 52 percent of her first serves while losing her first set in the tournament.
"When we went inside, I had one positive and one negative," said Clijsters, who reached the quarterfinals of last year's tournament, her first since coming out of retirement. "Actually, I felt comfortable playing my groundstrokes. That was good, because my serve was nowhere to be found. When we came back out, I knew I had to battle throughout, because you're not starting 0-0. You have to be ready to go."
Sharapova started feeling pain in her left heel in the last games of the second set, after the 74-minute rain delay. Sharapova didn't know if the injury would keep her out of this week's tournament in Montreal.
"I haven't really had any time to talk with the trainer or the doctor and see how it is," she said. "It just kind of flared up out of nowhere, so we'll see how it is."
Clijsters, playing in her first tournament since taking a month off following Wimbledon, seemed unfocused in the first set. She hit just five winners, half of Sharapova's 10, and committed 17 unforced errors while double-faulting seven times while Sharapova was serving three aces.
The two-time U.S. Open champion continued to struggle in the second set. She already was down a break before saving the three match points on her serve in the ninth game as the incoming weather front produced flag-whipping winds, darkened the skies enough to get the lights turned on and produced a downpour that stopped play.
"I think it certainly gave her time to relax," Sharapova said. "More than the conditions themselves, I think it was about just maybe her going in and having a chance to think about what she needs to do differently. She came out and started playing really good tennis."