Welsh head coach Lyn Jones makes seven changes to his side, with Tom Arscott returning from injury at full-back and Tom Voyce moving to the wing.
There's a change in the centres with Gavin Henson partnering Sonny Parker, while Gordon Ross takes over the number ten jersey and Nick Runciman starts at scrum-half.
There are two changes in the forwards: Tom Bristow starts at loosehead in place of Franck Montanella and Lee Beach comes into the side at number eight for Alfie To'oala.
Welsh take to the field on Sunday with five former Bath players in their starting XV - Nick Scott, Tom Voyce, Paulica Ion, Martin Purdy and captain Jonathan Mills - plus another on the bench in Billy Moss.
Head coach Jones said: "We've got Bath and what's important is how we turn up for Bath (after his side's 29-19 defeat to Wasps last week). They're a very good side with some good overseas signings."
Meanwhile, Matt Banahan will make his first appearance since the second round of the Premiership as he returns to the Bath starting line-up.
Banahan comes into the outside centre shirt, partnering Ben Williams. Tom Biggs and Kyle Eastmond continue on the wings, with Nick Abendanon at full-back. Stephen Donald and Michael Claassens also continue their half-back partnership.
Anthony Perenise starts at tighthead in place of David Wilson, scrumming down with Lee Mears and Paul James in the front row. Dominic Day and Dave Attwood combine in the engine room once more.
In the back row, injuries to Carl Fearns and Francois Louw see Club captain Stuart Hooper start on the blindside flank, with Will Skuse making his first Premiership start on the openside. Ben Skirving continues at the back of the scrum.
Bath head coach Gary Gold said: "I don't think you can really read much into the pre-season result (when Bath won 40-31), this will be a very different game.
"They're a good group of players, are well coached and have a great attitude to work hard for each other - I've been impressed by what they've done this season."
London Welsh: 15 Tom Arscott, 14 Nick Scott, 13 Sonny Parker, 12. Gavin Henson, 11 Tom Voyce, 10 Gordon Ross, 9 Nick Runciman, 8 Lee Beach, 7 Michael Hills, 6 Jonathan Mills (c), 5 Matt Corker, 4 Martin Purdy, 3 Paulica Ion, 2 Neil Briggs, 1 Tom Bristow.
Replacements: 16 Dan George, 17 Bill Moss, 18 Arthur Joly, 19 Adam Brown, 20 Mike Denbee, 21 Tyson Keats, 22 Seb Jewell, 23 James Lewis.
Bath: 15 Nick Abendanon, 14 Kyle Eastmond, 13 Matt Banahan, 12 Ben Williams, 11 Tom Biggs, 10 Stephen Donald, 9 Michael Claassens, 8 Ben Skirving, 7 Will Skuse, 6 Stuart Hooper (c), 5 Dave Attwood, 4 Dominic Day, 3 Anthony Perenise, 2 Lee Mears, 1 Paul James.
Replacements: 16 Brett Sharman, 17 Charlie Beech, 18 Kane Palma-Newport, 19 Will Spencer, 20 Guy Mercer, 21 Mark McMillan, 22 Sam Vesty, 23 Horacio Agulla.
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