Mikel Arteta’s side conceded just 29 goals in the Premier League last season and the Gunners pride themselves on their wall at the back.
With Leandro Trossard shown a second yellow card just before half-time, Arsenal set out to defend their 2-1 lead with everything they had in the second period.
“The space is not there in the team, they equalise the team. Kova [Kovacic] and Ruben [Dias] is destined for the shot,” said Guardiola.
“With Rodri it may have been different or maybe I put Ruben on the right. That’s why I delayed the sub for Kyle [Walker], but Kyle has a really good shot and crosses.
“Grealish created space. Raya made two, three or four saves [and] the second ball was not with us. It’s difficult.
“Congratulations to Arsenal, to be so strong mentally to block, it’s not easy but at the same time we were not easy to do it.”