Tennis great Williams, 44, made her eagerly-anticipated comeback at the London venue on Tuesday, securing a win alongside Canadian teenager Mboko in their first doubles match.The duo defeated third seeds Nicole Melichar-Martinez and Erin Routliffe 7-6 (7/2), 6-2.They are now scheduled to face Leylah Fernandez and Laura Siegemund on Thursday in the grass-court event, a warm-up for Wimbledon.Mboko, who received a bye into the round of 16 for the Queen's singles, was down a set but leading Karolina Pliskova 4-3 in the second when she slipped behind the baseline trying to return a shot.The stumble effectively forced her into doing the splits, drawing a gasp from the crowd.Mboko was visibly upset as she spoke to the attending medical staff.She got to her feet but the official reason subsequently given for her retirement was a left knee injury, with Mboko heard saying on television cameras "there is no stability right now".Mboko buried her face behind a towel as she continued to consult her team, before the umpire eventually announced her retirement, with the crowd giving the 19-year-old a sympathetic reception.If Mboko withdraws from the doubles, that will be the end of Williams's tournament as well.Williams, a 23-time Grand Slam singles champion, stunned the sporting world a week ago with her shock announcement she would compete at Queen's, where she is only playing in the doubles.