Arsene Wenger's side temporarily moved top of the Premier League last Saturday after coming from behind to beat Stoke at the Emirates Stadium.
But a week is a long time in football and back-to-back 2-1 defeats at Everton and Manchester City now leaves them nine points behind leaders Chelsea.
Arsenal led both matches only to have their soft underbelly exposed, with Walcott, who opened the scoring at the Etihad Stadium, underlining the importance of staying fully focused throughout.
"We haven't started the second halves very well," Walcott said.
"In previous games leading up now, we have actually played better in the second half and been on the front foot.
"But yesterday we were on the back foot and obvious Man City dominated the ball.
"We didn't create any chances in the second half to be honest so are disappointed in that sense but you have got to give credit to City because they played some very good football at times and we found that difficult."
Source : PA
Source: PA