Rain has ended play for the day with Venus and Klaasen trailing the German wildcard pairing of Tim Puetz and Jan-Lennard Struff 5-4 in the first set with the Germans serving for the set.
The match will resume overnight.
New Zealand's top ranked singles player Rubin Statham has been beaten in the first round of the US $75,000 ATP Challenger tournament in Fergana in Uzbekistan.
Statham lost after a strong start against Japanese qualifier Shuichi Sekiguchi, 0-6 7-6 (5) 6-2.
But there's been some good news for young women's pro Paige Hourigan in the US.
Playing in just her second ITF tournament, the 21-year-old has won through qualifying to reach the main draw in Baton Rouge Louisiana.
Hourigan has beaten American Kennedy Shaffer 6-2 7-5 in one hour 59 minutes. She will face Argentina's Maria Lourdes Carie in the first round.