Beltran homered from both sides of the plate and reached all parts of the ballpark with his three two-run homers: straightaway center in the first, deep left in the seventh and into the right-field seats in the ninth.
This was quite a gratifying afternoon for a player who's been hampered in recent seasons with knee injuries. He felt like a kid again.
"I never smile a lot, but I was smiling," Beltran said. "It's going to be a day I'll never forget."
The switch-hitting outfielder became the eighth Mets player to hit three in a game, and first since Jose Reyes on Aug. 15, 2006, at Philadelphia.
And the Mets needed all his offense, too, especially with first baseman Ike Davis going on the 15-day disabled list because of a sprained left ankle and bone bruise, and with third baseman David Wright sitting out to rest a sore neck and back.
"He was a one-man wrecking crew today," Wright said. "That's a monster day."
Reyes hit a two-run single in the fourth that chased Jimenez (0-3) from the game and kept the Rockies ace searching for his elusive first win of the season. He lasted just 3 2/3 innings in his shortest stint of the season, surrendering five runs and three hits while tying a career high with six walks.
"I was trying to be a little bit too fine," Jimenez explained. "I was trying to hit the corners instead of throwing the ball down the middle and making them swing the bat."
With San Francisco beating Arizona earlier in the day, Colorado fell out of at least a tie for the lead in the NL West for the first time since April 5. The Rockies have now dropped six of their last seven contests, including two of three against the Mets, a team they swept in a four-game series at Citi Field last month.
"We deserved to fall out of first place today with the way we played," Todd Helton said. "Hopefully, it will be a wake-up call for us and we'll turn it around soon."
Niese was pulled with one out in the seventh as the lefty gave up three straight singles, including a run-scoring liner up the middle by pinch-hitter Alfredo Amezaga. Michael O'Connor came in and allowed a two-run double to Seth Smith, cutting New York's lead to 7-5.
Tulowitzki had been swinging a hot bat against the Mets, too -- five of his nine homers this season have been against New York hurlers.
Jason Isringhausen pitched a rocky eighth, giving up a walk and a single to begin the inning.
Beltran's third homer of the game in the ninth gave the Mets a four-run cushion, making Francisco Rodriguez's appearance a non-save situation.
The game was delayed for 2 hours, 10 minutes as a spring storm moved through the area for a second straight day. The mixture of rain and snow that fell Wednesday led to the finale of the three-game series being pushed back 24 hours, keeping the Mets in the Mile High City an extra night and leaving the team scrambling to locate an extra night's lodging as they switched hotels.
The Mets were forced to juggle around their lineup Thursday with Davis out and Wright resting.
Daniel Murphy, who has been playing second, moved to first, and Justin Turner took over Murphy's spot. Willie Harris started in place of Wright and helped set the table for Beltran's blasts. He was on base ahead of Beltran each time, finishing the game with three walks and a single.
It didn't take long for the Mets to jump all over a struggling Jimenez. After Harris walked in the first, Beltran drove a 93-mph fastball to deep center.
This was the fifth time Beltran has homered from the left and right side in a game as a member of the Mets, tying him with Todd Hundley for the most in team history.
"To hit a home run to all fields, from both sides, I've never seen anything like it," Mets manager Terry Collins said.
Jimenez has hardly been his All-Star self this season. His blazing fastball has been very hittable and his pinpoint command spotty, in part because of a bothersome cracked cuticle on his pitching thumb.
Jimenez showed signs of getting back on track in his first quality start of the season last Friday at San Francisco, but then struggled against the Mets.
"The only thing I can do is keep working hard every day," Jimenez said. "I'm not going to get frustrated. I'm not doing anything good for the team, but hopefully there's a time where I'll start doing good."