The province's 21-year-old centre David McSharry hangs on to the number 12 jersey after an impressive display at Ravenhill. The half-back pairing of Paul O'Donohoe and Miah Nikora is also retained.
In the pack, the front row remains the same with Adrian Flavin joined by Ireland Wolfhounds prop Brett Wilkinson and New Zealander Rodney Ah You.
The second row pairing of Michael Swift and Mike McCarthy stays in place. Swift shook off a knock that saw him depart the pitch early last Saturday and looks set to win his 205th cap for the province.
There is a new back row with number 8 George Naoupu joined this week by former skipper John Muldoon and Ray Ofisa who both return to the starting line-up.
It is an experienced side with five centurions in the pack - Wilkinson, Flavin, McCarthy, Swift and Muldoon - along with Duffy in the backs.
The replacements see Henry Fa'afili return to the squad after a knock that kept him out of the Ulster games. He joins Niall O'Connor and Frank Murphy as the reserve backs, both of whom have featured in the Heineken Cup previously with Ulster and Leicester Tigers respectively.
Ethienne Reynecke, Ronan Loughney and Dylan Rogers make up the front row replacements, and David Gannon and Thomas Anderson have also made the matchday panel.
CONNACHT (v Harlequins): Gavin Duffy (capt); Brian Tuohy, Eoin Griffin, David McSharry, Tiernan O'Halloran; Miah Nikora, Paul O'Donohoe; Brett Wilkinson, Adrian Flavin, Rodney Ah You, Michael Swift, Mike McCarthy, John Muldoon, Ray Ofisa, George Naoupu.
Replacements: Ethienne Reynecke, Ronan Loughney, Dylan Rogers, David Gannon, Thomas Anderson, Frank Murphy, Niall O'Connor, Henry Fa'afili.