The 24-year-old scored the only goal of the game at the Emirates Stadium, boosting his team's chances of qualifying for the Champions League.
He believes that the Gunners can win their remaining two games and seal third place in the Premier League.
"QPR deserve credit because they put us under a bit of pressure, but our defence has been solid for the last few months now," Walcott told BBC Sport.
"Can we win our remaining games? Without a doubt. The way we're playing as unit, we know we're always going to score goals. When the pressure is on us everyone steps up."
Arsenal take on Wigan Athletic at home on Tuesday before finishing with a trip to Newcastle United.