Gallinari scored 26 points – including a valuable three-point basket with 12 seconds remaining in the match – as the Nuggets won for the fifth time this season, and sent the Grizzlies to just their second loss.
It was a tight contest for the majority of the game, but Rudy Gay and Zach Randolph his some valuable shots in the final quarter as the Grizzlies started to take control.
The Grizzlies led by four (92-88) when Randolph hit a lay-up with a little over two minutes remaining, but that was to be their final score as Gallinari stepped up late.
While Gallinari was the star of the show for the Nuggets, he received plenty of support from his more than capable support cast.
Big man JaVale McGee added 15 off the bench, while Kenneth Faried (13) and Corey Brewer (10) also scored in double figures.
Gay led the way for the Grizzlies with 22 points, while Spaniard Marc Gasol had 16.
Meanwhile, in Charlotte, the Bobcats continued their impressive start to the campaign with a 102-98 victory over the Milwaukee Bucks.
The Bobcats exploded out to a 30-23 quarter-time lead, but fell behind by four at the final change as Monta Ellis scored at will for the Bucks.
But Ramon Sessions and Michael Kidd-Gilchrist hit their straps in the final term to ensure the Bobcats got home for their fifth win of the season.
Sessions top-scored for the Bobcats with 23, while Ellis had a game-high 31 for the Bucks.
Ellis’ former team, the Golden State Warriors, also registered an upset victory on Monday as they beat the Dallas Mavericks 105-101 on the road.
The Warriors led by five at half-time, but the Mavericks came roaring back into contention on the back of some impressive shooting from O.J. Mayo.
Mayo hit seven straight points for the Mavericks during the final term to ensure the game went into extra-time, but Curry stepped up in the additional period as the Warriors won for the sixth time.
Curry’s 31-point haul was a game-high, while Mayo led the way for the Mavs with 27.
In other matches on Monday, the Atlanta Hawks downed the Orlando Magic 81-72, the Indiana Pacers beat the Washington Wizards 96-89, the Utah Jazz thrashed the Houston Rockets 102-91 and the Los Angeles Clippers won 92-87 on the road in San Antonio.