Crawford beat his previous career high of 39 points set against Miami on March, 30, 2011, when he was with Washington. He surpassed it with a runner that put the Warriors ahead for good at 110-108.
Randy Foye, who led Denver with 32 points, raced downcourt in response but his finger-roll rimmed out and Golden State corralled the rebound.
With 30 seconds left, Barnes sank a free throw and Draymond Green swooped in to tip in his errant second shot, giving the Warriors a 113-108 lead.
Crawford and Steve Blake each missed a free throw over the next 14 seconds, giving the Nuggets an opening. Green was whistled for goal-tending on Foye's 3-pointer with seven seconds left but the call was overturned upon review, leaving the Nuggets trailing 115-112.
The Warriors are headed to their second straight Western Conference playoffs, again as the No. 6 seed and this time, they'll face the third-seeded Clippers starting Saturday in Los Angeles.
With Andrew Bogut out indefinitely and nothing to play for as far as seeding, the Warriors rested their regulars for the playoffs. Guard Klay Thompson was the only starter coach Mark Jackson put in his starting lineup 48 hours after Golden State secured its first 50-win season since 1993-94.
Thompson played just eight minutes but his was an efficient cameo with eight points. Green was pressed into duty in the fourth quarter when Hilton Armstrong fouled out.
Nuggets coach Brian Shaw had no problem with his counterpart going with a short bench by design, something Denver has had to do out of necessity for much of the season because of a rash of injuries to the likes of Ty Lawson, JaVale McGee, Danilo Gallinari, J.J. Hickson and Nate Robinson.
''It will be like playing ourselves,'' Shaw said before tip-off. ''We'll get to see what it's like.''
The Warriors' reserves had fresh legs and continually beat the winded Nuggets downcourt. By halftime, Golden State, despite shooting just 9 of 17 from the foul line, was ahead 66-52 behind 22 points from Barnes and 19 from Crawford.
The Nuggets opened the fourth quarter on a 12-2 run to take the lead and give the home crowd something to cheer about.
This marked the final game for Nuggets trainer Jim Gillen, who never missed a game or a practice in 23 seasons with the Nuggets. He worked for nine head coaches and four interim coaches, five general managers and nearly 200 players, taping up, by his estimate, 15,000 ankles.
Shaw called Gillen the fabric of the franchise.
''As a first-year head coach, I've had to rely on him in so many different situations from his experience and knowledge and know-how from things that we need to get together on, from hotel stays to when we need to get together and practice and how much rest guys need and to even in-game strategy, timeouts at the end of the game and things like that,'' Shaw said.
NOTES: As expected, Lawson (sprained ankle) did not play in the season finale, meaning he missed the last seven games of the season. ... The visiting team won all four games in the season series.
Follow AP Sports Writer Arnie Melendrez Stapleton on Twitter: http://twitter.com/arniestapleton