The American world number one broke Flipkens on her first service game and then went on to systematically attack the Belgian’s second serve and triumph 6-3.
“It was fun. She played really well and she made it really entertaining for the crowd and I was happy to be there. The crowd was pumped. I was pumped,” Williams told reporters.
Williams and Lleyton Hewitt, playing for the Singapore Slammers team, earlier lost their mixed doubles match against Flipkens and Andy Murray of the Manila Mavericks team 1-6. But the powerful American got into her rhythm as the evening wore on.
Williams, who last played at the WTA Finals in Singapore, winning the tournament on October 26, admitted she was rusty at first following the break.
“Yes, it was a factor initially, but it’s good to get some match play,” she said.
“You have to just go the second you land (even though) you have this jet-lag.”
The team-oriented IPTL format, which has attracted many of the world’s top players, features ties consisting of five one-set matches.
Williams will also play in the Singapore leg of the IPTL tour from December 2 before starting her training for the regular 2015 women’s tour.
For world number six Murray, the mixed doubles win was his first in the IPTL tournament.
He later went on to beat Williams’ Singapore Slammers teammate Nick Kyrgios 6-5, after a five-minute shootout to break a 5-5 tie.
“It was nice to finish the weekend with two wins today,” Murray told reporters.
He had lost to world number nine Marin Cilic of the UAE Royals team Friday and Gael Monfils of the Indian Aces team on Saturday, while his mixed doubles partnership with Maria Sharapova also brought two consecutive losses.
After Singapore the IPTL tour moves to New Delhi before concluding the year in Dubai.