Navarro scored 28 points and Gay added 27, and Memphis handed the Washington Wizards a 124-118 loss Saturday night.
Jamison finished with a season high for points and 11 rebounds for the Wizards, who lost their second straight following six straight victories.
"We still had an opportunity, a chance to crack into the game ... but we just fell a little short," said Caron Butler, who had 27 points for Washington.
Navarro matched his career high for scoring, while Gay hit 11 of 19 shots from the field after going 12-of-41 in the previous four games.
Navarro was picked by Washington in the second round of the 2002 NBA draft but spent his career overseas before the Grizzlies traded a future first-round pick for the rights to him this year.
"I was really looking forward to doing well and playing well against the team that drafted me," Navarro said. "I was really looking forward to this game."
Butler said the Wizards' weakness on defense helped Navarro with his 5-of-8 shooting from 3-point range.
"He's one of those guys if he gets his feet set, you can pretty much count it," Butler said.
Jamison shot 18-of-22 from the floor.
"He is strong and he keeps on moving," Gay said. "He gets his position and he keeps moving. It's tough to guard."
With 11 rebounds, Jamison became one of 12 active NBA players with 12,000 points and 5,000 rebounds.
"I've been known to find a way to make the ball go in the basket," Jamison said. "Offensively, we're doing a good job moving it and the ball was just going in."
The Grizzlies scored a season-high 25 fast-break points, and coach Marc Iavaroni said he was happy with the quicker tempo.
"I thought Lowry was a key to that," Iavaroni said. "He made progress tonight, even though he did get six turnovers. I think he was instrumental in the stretch when we took the lead."
Memphis held the biggest lead of the night for either team, 14 points at 101-87 with 6:10 to play. The Wizards got to 122-118 when Jamison scored inside with 13 seconds left, but could get no closer.
Lowry kept the Grizzlies in front with eight points in the final two minutes, including six straight free throws. He finished the night 13-of-14 from the line.
Both teams had success from long range. The Grizzlies shot 45 percent beyond the arc. Just as Navarro, Miller also made five of eight 3-pointers.
The Wizards shot 53 percent from long range. Butler was 3-of-5, with all three baskets coming in the final 1:02.
The Wizards were again without leading scorer G Gilbert Arenas who had surgery on his left knee Nov. 21. ... Washington was playing the first of four road games before returning home for eight of the next nine. ... Memphis C Darko Milicic missed his fifth game with a sprained left thumb and Memphis G Mike Conley remained sidelined with an injured right shoulder. ... The Wizards wore their alternate gold and black uniforms for their first time of the season. Last year they were 8-7 in those uniforms.
No. 1 draft pick Ben Simmons said hearing the news of the death of his cousin "is a reminder to never forget the important things in life."
DeMar DeRozan, arguably the top shooting guard who could hit the free-agent market, is focused on re-signing with the Raptors, a source said.
Cavaliers point guard Kyrie Irving has accepted an invitation to play for Team USA at the Summer Games, filling out the 12-man roster for Rio de Janeiro.