Serena Williams lost a super tie-break to Jelena Ostapenko but showed glimpses of her dominant best in the former world number one's first appearance after becoming a mother in September.

The 36-year-old had not played competitively since winning her 23rd grand slam singles title at the Australian Open in January, but is set to return to the WTA Tour in 2018 and defend her crown in Melbourne next month following the birth of her daughter, Alexis.

Ostapenko, this year's surprise French Open winner, triumphed 6-2 3-6 10-5 in their exhibition contest at the Mubadala World Tennis Championships on Saturday, in what was the first meeting between the pair.

Both players showed signs of rustiness early in the match, coughing up their serve in each of the opening games.

It was the returning American who took longer to get up to speed, offering flashes of her familiar best with a handful of heavy forehands but holding serve just once to allow Ostapenko to take control.

Having shaken off some cobwebs, Williams then asserted herself, breaking four times to take the second set, with the highlight a crunching forehand return winner off Ostapenko's first serve that kissed the line and left her opponent helpless.

Williams' inconsistency on serve hurt her as she fell 0-5 behind in the deciding super tie-break, fighting back to 8-5 before the world number seven wrapped it up.

Speaking in an on-court interview after the match, Williams said: "Motherhood's phenomenal. I was a little worried out there, [thinking] 'is it going to be ok?'. [But] it's good to be back on the court."

Earlier in the day in Abu Dhabi, Dominic Thiem broke Pablo Carreno-Busta twice and did not give up his own serve on the way to a 6-3 6-4 victory in 69 minutes.