Manchester City moved 16 points clear of United at the top of the Premier League table after a 3-0 win over Arsenal at the Emirates Stadium.
Guardiola praised his team for having the determination in the league just four days after beating the Gunners to win the Carabao Cup final.
"Mentally we were strong," said the Spaniard. "We were clinical. We scored three outstanding goals. After that it was not easy - the first 15 minutes of the second half we were poor. Still, it's an amazing result for us."
"We are out of the FA Cup and we won the League Cup. Now it's just two competitions and you fight for one of them for 10 months. These are the last steps to be champions, you keep going until the end."
Guardiola is targeting five more wins as City close in on the Premier League title for the first time since 2014. "We have to win five games," he said. "We don't think too much. Now we play Chelsea. Hopefully we have the desire to win, to be the best team in England."
"We forget that we are tired. It’s so difficult to win two games in a row in three or four days against a team like Arsenal and it can be so complicated. The conditions were also tough. But 3-0 and 3-0 here it was so important here. We need five games to be champions and we're getting closer."