The argument can be made the Denver Nuggets are what the Celtics now strive to be — a balanced team with any number of scorers who can make a spike in a box score. The Nuggets are also young, quicker and more athletic — far better equipped for three overtime periods than their revamped elders on the Celtics. But youth flinched first last night. Kevin Garnett, despite one of his worst shooting nights of the season, recovered with six points in the third overtime to complement Jason Terry’s game-winning 3-pointer in a 118-114 C’s win at the Garden. It was the Celtics’ ninth overtime game of the year and the fourth to reach at least two overtimes. The C’s improved to 5-4 in overtime, with a double-overtime win over the Miami Heat and last night’s game included in their current seven-game win streak, the longest of the season. Denver, which had been the NBA’s hottest team, finally hit the wall last night after nine straight wins. There were plenty of front-rimmed jumpers and air balls to go around last night. Despite their need for deep-tissue massage after the win, the grayer Celtics seemed to thrive on being the team closer to cashing in their 401(k) accounts. “I’m tired after every game,” Paul Pierce said when asked if he was tired after playing 54 minutes, the most on either side. Terry joked about Garnett being 50 years old. And Garnett talked in a slow, staggering cadence. Garnett admitted to hearing about Terry’s jab. He didn’t bother to contest it, either. As coach Doc Rivers later revealed, Garnett started the second overtime on the bench in an attempt to regain some energy.