The Algerian was outstanding at the London Stadium, a danger throughout with his ability to go past defenders and find a pass.
The manager was clearly impressed and feels his performance sends a message to Bernardo Silva that he will have a fight on his hands to keep his place in City's attack this season having been a regular during the Fourmidables campaign.
“The only problem Riyad had last season is the manager didn’t select him often because he had one of the best players of the season, Bernardo [in his position],” Guardiola said.
“Bernardo now knows ‘wow, Riyad is an incredible player’ and has to make a step forward. Gabriel came back with incredible speed and energy, so Sergio has to know ‘wow, Gabriel is in top form’.
“It’s the only way to maintain our levels. We realise that is the reason why we did what we did last season. Every player has to know it.
“Today on the bench we had Joao, Gundogan – the best midfielder of the last two months last season, without him we couldn’t have achieved what we did. We had Foden, a talented player, we had Bernardo. Sergio as well. Fernandinho is at home.
"It’s the only way. If the players don’t play good then I have to think others deserve it. They have to play good, to show respect to the players who aren’t playing. That’s what I know from my experience as a manager to have the team together and focused.
“Otamendi as well, just two training sessions made an incredible performance in the Community Shield. That’s the reality.”
Guardiola also praised Mahrez’s dedication to the cause.
The winger played a key role as Algeria lifted Africa Cup of Nations this summer, a tournament that finished just three weeks before the start of the Premier League season.
But despite his heavy involvement in the competition, Guardiola revealed Mahrez called him immediately after it ended to say he wanted to Manchester return as soon as possible to begin preparations for the new season.
“Riyad called me after the Africa Cup of Nations to say he only needed 10 days’ rest,” Guardiola said.
“He wanted to come back soon and he wanted to play. I like it!
“I wanted to play him here [at West Ham]. Bernardo has nothing wrong but a little muscular problem.
“Everybody has to know that I trust all of them. That is the truth. After four seasons, if I didn’t like a player, he wouldn’t be with us. We’d loan or sell him.
“They have to compete with each other. With the opponents, yes, but compete with each other.
“When they play they have to know they need to play good. You want to play next week? You have to play good.
“That is why we maintain our high standards. We have to feel the pressure. If you don’t then there is a tendency to be more relaxed, sloppy like the first half.”