Tony Parker added 20 points, and Willy Hernangomez and Marvin Williams 16 for the Hornets.
T.J. Warren had 23 points, Josh Jackson 22 and Deandre Ayton 19 for Phoenix. Jamal Crawford scored 16. The Suns' Devin Booker left the game with back spasms in the second quarter and did not return.
Phoenix fell to 0-6 with one game left on a seven-game homestand. The Suns had won five of seven when the homestand began.
The Hornets were on the second stop in a season-high, six-game road trip that began with a loss at Denver on Saturday night.
Walker was 5 of 8 from the field and 7 of 8 on free throws in his late surge, which ended with a basket at the final buzzer from just inside midcourt. Initially it was waived off but allowed after a video review.
Charlotte outscored Phoenix 11-4 over the last 1:17, with Walker scoring all of them, after Crawford's 20-footer put Phoenix up 109-108 with 1:21 to play.
Neither team led by more than eight points in the tight contest.
There were 13 ties and eight lead changes in the first half, with neither team up by more than six points, and the Suns were ahead 60-57 at the break.
Ayton had 15 points and seven rebounds in the first half.
Charlotte took an 85-81 into the fourth quarter before the Suns tied it 85-85 on De'Anthony Melton's 3-pointer from the corner with 11:02 to play.
Parker started the subsequent 8-0 run with a layup and ended it with a 16-footer that put Charlotte up 93-85 with 8:55 to play.
The Suns came back and repeatedly cut the lead to one before Crawford's basket finally gave them the lead.
But four seconds later, Walker converted a three-point play and the Hornets were back on top for good.
Hornets: Charlotte swept the season series with Phoenix 2-0 last season. ... Walker ranks second to LeBron James in fourth-quarter scoring at 8.27 points per game. The Suns' Booker is third (7.50). ... Charlotte doesn't play another home game until Jan. 17 (Sacramento). ... The Hornets won for just the third time in nine games.
Suns: Crawford joined Dell Curry as the only NBA players, since starting lineups were recorded, with 11,000 career points as reserves. ... Booker's back problem brought an end to 11 consecutive 20-point games for the Phoenix star guard, the second-longest such streak of his career. ... Phoenix entered the game fourth in the NBA in steals at 8.98 per game.
Hornets: at Los Angeles Clippers on Tuesday.
Suns: host Sacramento on Tuesday
Hornets: at Sacramento on Monday night
Suns: host Sacramento on Tuesday night
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