The small forward out of North Carolina State shot a sizzling 10-for-16 (62.5 percent) from the field Saturday and scored a team-high 22 points, getting buckets mostly off drives and mid-range jumpers.
Warren, the 14th overall selection in the 2014 draft, also added four rebounds, a block and a steal in more than 23 minutes.
Also impressive for Phoenix was second-year Archie Goodwin, who posted 17 points on 6-for-10 shooting from the floor and 5-for-7 from the free throw line.
Center Miles Plumlee grabbed nine rebounds in just under 27 minutes, but he finished with just three points. Both he and rookie Alec Brown, Phoenix's lone second-round selection (50th overall) in 2014, went 0-for-7 in the game.
The Suns had trouble shutting down Golden State guard Justin Holiday, who had a game-high 29 points in 32 minutes.
In a rematch of last year's Las Vegas Summer League championship game, Saturday's contest went down to the wire. Goodwin made a steal and a fast break layup to put Phoenix up 72-70 with just under a minute left, but the Warriors scored the next two buckets, capped by Holiday's putback layup with three seconds left, to go up by two. Goodwin attempted a three-pointer as time expired but missed.
Golden State is now 2-0 in Summer League, while the Suns are 0-1.
Phoenix will face the Milwaukee Bucks (0-1) Sunday at 7 p.m. MST.