The conclusion of the congested festive schedule saw a tired display by the Londoners, who looked set to draw a blank for the second straight home game before Bendtner bundled home in the 88th minute and Walcott wrapped up the points in stoppage time.
Manchester City had briefly gone top after subduing a battling Swansea City 3-2 away while Chelsea beat Southampton 3-0 on the road and Liverpool won 2-0 at home to Hull City.
Fernando Torres became the first Chelsea striker to score a league away goal in 13 months as they maintained their title push and Christmas Day leaders Liverpool regained a top-four spot as Luis Suarez netted for the 20th time this season.
Arsenal, with 45 points from 20 games, stayed one point clear of Manchester City and two ahead of Chelsea in third with Liverpool a further four points off the pace.
Everton's Leighton Baines converted an added time penalty to rescue a 1-1 draw at Stoke City, although the Merseysiders still dropped to fifth, while 10-man Newcastle United stumbled to a 1-0 defeat at West Bromwich Albion.
At the bottom, Fulham edged 10-man West Ham United 2-1 with the east London side staying second-bottom above Sunderland, who lost 1-0 at home to Aston Villa. Crystal Palace are 18th after a 1-1 draw with 15th-placed Norwich City.
Champions Manchester United host Tottenham Hotspur in the late game.
BENDTNER STRIKES
After Arsenal's last home game ended in a goalless draw against Chelsea, the home fans were fearing another shutout at The Emirates that would have shunted them off the top.
Cardiff City, playing in front of Ole Gunnar Solskjaer, who sat alongside owner Vincent Tan and is expected to become their new manager, defended stoutly for 88 minutes before their resistance was ended by second-half substitute Bendtner.
The Dane scored from close range after Cardiff keeper David Marshall saved a Bacary Sagna header, and Walcott then rubbed salt in the Welsh club's wounds by converting Jack Wilshere's excellent pass.
The result kept Manchester City at bay after they showed their title credentials with a fifth consecutive league win.
City came out on top thanks to second-half strikes from Yaya Toure and Aleksandar Kolarov after Swansea's Wilfried Bony had cancelled out Fernandinho's early opener.
Bony grabbed a stoppage-time consolation for Swansea who are now without a win in six league games.
Manchester City, who recorded back-to-back away league wins for the first time this season, have taken 25 points from their last 27 and scored 57 goals in the opening 20 games to lay down a marker in the congested tussle at the top.
Chelsea's misfiring forwards had failed to find the target away from Stamford Bridge during the whole of 2013, but the hoodoo was broken on the hour at St Mary's when Spaniard Torres headed home from close range.
Willian smashed home a second from the edge of the area and fellow substitute Oscar, who had a hand in all three goals, added the third with a clinical finish after being sent racing through on goal.
SUAREZ STUNNER
If Chelsea's strikers have been struggling, Liverpool have one who cannot stop finding the back of the net.
Suarez made the game safe against Hull with a stunning free kick into the top corner for his 15th goal in seven home games this season. It was the seventh successive match at Anfield that the Uruguay striker had found the net.
A Daniel Agger header had put Liverpool on their way to victory after back-to-back away defeats by Manchester City and Chelsea over the Christmas period.
"It was arguably our best win of the season, on the back of what was a tough schedule for us with a light squad," Liverpool manager Brendan Rodgers said. "The energy, as you'd expect, was not what it has been but we showed great resilience today."
Stoke's Liverpool loanee Oussama Assaidi gave his parent club a helping hand with the opening goal against Everton but Baines equalised from the spot after Jermaine Pennant fouled Leon Osman.
West Ham went ahead after seven minutes against relegation rivals Fulham but it all went wrong from the 32nd when Steve Sidwell equalised and 12 minutes later visiting captain Kevin Nolan was sent off for kicking out at Fernando Amorebieta.
After laying siege to West Ham's goal, Fulham's Bulgarian striker Dimitar Berbatov poked home midway through the second half to make it 2-1.
Gabriel Agbonlahor scored the winner for Villa at Sunderland while Newcastle had Mathieu Debuchy sent off against West Brom, who recorded their first league win in 10 games thanks to Saido Berahino's late penalty.
Norwich City also had a man sent off at fellow strugglers Crystal Palace with Leroy Fer dismissed late on for a second booking. Palace's Jason Puncheon equalised with a penalty after Bradley Johnson had curled in the opener for the Canaries.
