Captain Adam Thomas and dangerman James Davies suffered knocks on the narrow Sam Boyd Stadium pitch which suited teams with a physical approach which left Wales battening down the hatches.
Wales managed to regroup and beat USA in the Bowl quarter-final with tries by Luke Morgan and Dylan Morgans edging Wales home 12-7 but they ran out of legs in the semi-final against Fiji with the South Sea Islanders prevailing 40-12.
Wales will be seeking revenge in Wellington's Westpac Stadium on Feb 7-8, having drawn series leaders South Africa again alongside England and Portugal.
Wales head coach Gareth Williams will be without Thomas for the Wellington Sevens as he is heading home after suffering a recurrence of his injury and will be replaced by Iolo Evans.
Williams declared the Las Vegas tournament as a 'mixed' weekend with games being won and lost on the smallest of margins.
"We started positively against South Africa, but one error resulted in a Blitzbokke try and they maintained their momentum to finish with a heavy score!
"Individual error and some bad luck resulted in us needing to score with the last play of the game versus Kenya. We showed good composure to get the ball over the line, but a superb last ditch tackle on James Davies resulted in a lack of control placing the ball.
"Canada staged an excellent second half comeback against us, but we were disappointed with our own game management, especially when down to six men.
"The boys showed good quality and character, after losing Thomas in the first minute and Davies in the Canada game, to overcome a highly motivated home USA side. Dylan Morgans scoring a well -made try with the last play of the game."
Williams then added the younger players were taught a harsh lesson against Fiji in the Bowl semi-final.
"Fiji proved a game too far. Despite taking the lead and causing them problems, a lack of focus at stages during the game gifted Fiji tries that pulled them away from us. It was a good lesson for a number of young players that each second is so vital on a Sevens pitch.
"It was disappointing to leave with one win, but it could easily have been so different. The challenge for the next two weeks in the lead up to Wellington is to refine everything that was good and tighten up on our concentration levels throughout games. There were some excellent examples of execution on what we have been working on, and then some silly errors that detract from that.
"On a better note, Will Price performed superbly in the centre, with the whole squad contributing positively at times during the weekend."