Williams, who must have been feeling at home in Connacht's all black second strip, was making his first start in the Challenge Cup for the province. The inside centre turns 27 on Wednesday.
Connacht full-back Daniel Riordan has his run halted by Harlequins duo Tani Fuga and Gavin Duffy. Ireland utility back Duffy, 25, lined out at outside centre on Friday night, showing up well at his former home ground.
Connacht winger Darren Yapp needes support as he is out-numbered by four to one. The 31-year-old Yapp made his Challenge Cup debut for Bristol Shoguns back in 1997.
Chris Keane, Connacht's sparky scrum half, has his midfield break snaffled by Andre Vos and Mike Ross of Harlequins. Well-built prop Ross, who played on the tighthead side of the 'Quins scrum, has successfully made the switch across to London after helping Cork Constitution win the AIB Cup last season.
Matt Mostyn, who penned a two-year contract extension with Connacht last March, is felled by Harlequins flanker and captain Paul Volley.
'Quins centre Jordan Turner-Hall gets to grips with Connacht's Colm Rigney, who had another barnstorming game from the base of the province's scrum.
Tani Fuga and Ceri Jones sandwich Paul Warwick as the Connacht out-half looks to offload at the Sportsground. Former Australian Sevens captain Warwick is Connacht's second top scorer in Challenghe Cup history behind Eric Elwood - after his contribution on Friday, he has now scored 143 points in 14 games.
Ted Robinson, who came on as a replacement for Mostyn and was also subbed on during Connacht's semi-final second leg win over 'Quins in April 2004, tries to keep hold of possession as Ceri Jones closes in.
**All photos by Dan Sheridan of Inpho Photography**