Laurent Koscielny admits Arsenal's ability to win when they don't play well will determine their title chances.
The Gunners are in scintillating form, having won their last seven matches in all competitions.
Next up is Middlesbrough at the Emirates, where a win would put the Gunners top - at least for 24 hours.
Koscielny isn't getting carried away though and believes Arsenal must grind out victories to finish top of the pile in May.
"If you want to be champions, you have to win the tough games," he told Sky Sports.
"The most important thing is to win games when you are not playing well. We need to come out of games saying: 'it was difficult, but we won 1-0'.
"It's important to have this during the season whenever we have bad moments or when it's difficult to play our football.
"In football, it's always difficult to play at the same level, with the same quality of passing and movement.
"Sometimes, you're in defensive positions more and have to fight with your team-mates to keep the clean sheet. You must adapt to different situations.
Arsenal's midweek win over Ludogorets also puts them in pole position to reach the knockout stages in the Champions League.
But Koscielny insists they must stay grounded, adding: "The squad is better, we are more experienced and we have played together a long time.
"The league is very long - it's a marathon, not a sprint. We can see from last season that it's difficult to stay high in the table."