Clijsters' victory took her win-loss record against Safina to 6-2
Kim Clijsters beat former world number one Dinara Safina 7-5 6-2 in a rain-hit Cincinnati Open second round.
The US Open champion and her Russian opponent had played only three games when they were forced off court for almost an hour by a downpour.
Sixth seed Vera Zvonareva sat through two rain delays totalling three hours and 28 minutes before overcoming Maria Kirilenko 7-5 2-6 7-6 (7-2).
Maria Sharapova advanced with a 6-3 6-1 win over Andrea Petkovic.
Third seed Elena Dementieva became the highest-ranked player to go out in Ohio, losing 6-1 6-3 to world number 25 Anastasia Pavlyuchenkova.
"I was not feeling well and I think I was affected by the weather," said the Russian after her exit.
"I think that was probably the worst match of mine for a long, long time. I was just not into the game. I couldn't really focus, my concentration was not there."
Pavlyuchenkova will meet 13th seed Shahar Peer of Israel, who defeated Spanish qualifier Nuria Llagostera Vives 6-3 6-2.
"I had nothing to lose against Elena and I just wanted to enjoy things and put on a good performance," said the 19-year-old, who won her second WTA event in Istanbul last week.
Danish second seed Caroline Wozniacki eased into the third round with a 51-minute 6-0 6-2 victory over Austria's Sybille Bammer, who hit 28 unforced errors.
French Open champion and fifth seed Francesca Schiavone of Italy continued her poor run of form since winning the title at Roland Garros and was beaten 6-4 6-4 by Russia's Elena Vesnina.
After taking the first three games of the match, Schiavone dropped six of the next seven to lose the first set.
Former world number one Ana Ivanovic, currently down to 62 in the world rankings, beat 32nd seed Yaroslava Shvedova 6-1 7-5, having seen off ninth-seeded Victoria Azarenka in the first round.
"I finished that first match strong and I just tried to take that into the match today," said the Serb.
Clijsters will next face unseeded American Christina McHale, who had a 6-2 6-4 win over Japan's Ayumi Morita.
Zvonareva will face Italian 11th seed Flavia Pennetta, who defeated Romanian qualifier Monica Niculescu 6-0 6-1 earlier in the day.