Gavin Duffy crossed for Connacht's second try in the second half, with Ian Keatley adding the extras but it wasn't enough to cancel out a brace of tries from London Welsh number eight Tom Brown and one from centre Tom Rock.
Connacht will conclude their preseason campaign on 26th August when they host the Queensland Reds at the Sportsground on Tuesday evening.
Tries: C Muldoon, Duffy
Tries: Rock, Brown (2)
T Nathan; F Carr, M Deane, A Wynne, K Matthews; A Dunne, K Campbell; J Lyne, C Muldoon, R Loughney; M Swift, A Browne; M McCarthy, J O'Connor, J Muldoon (C).
Replacements: I Keatley for Dunne, 23 mins; A Flavin for C Muldoon, 39 mins; B McGovern for Browne, 40+2mins; G Duffy for Deane, half time; C Rigney for Muldoon, half time; A Farley for Browne, half time; S Cronin for O'Connor, 59 mins; J O'Connor for Cronin, 66 mins; B Wilkinson for Loughney, 75 mins; S Cronin for Flavin, 75 mins.
E Lewis Pratt; A Jenkins, T Rock, P Mackey, P Sampson; A Thomas, A Walker; P Doran Jones, D George, A Liffchak; W Leweravu, M Powell (C); D Ball, T Audley, T Brown.
Replacements: J Mills for Audley, 34 mins; N Runciman for Walker, 52 mins; S Vuli Koto for George, 58 mins; M Corker for Powell, 58mins; M Odejobi for Jenkins, 64 mins; D Williams for Doran Jones, 64 mins; P Doran Jones for Liffchak, 69 mins; M Powell for Brown, 73 mins; A Liffchak for Doran Jones, 77 mins.
Referee: David Wilkinson