The Algeria winger was officially announced as a Man City player on Tuesday evening, penning a five-year contract at the Etihad Stadium following his move from Leicester City.
Mahrez joined the Foxes from Le Havre for £400,000 in 2014, and was named the PFA Players' Player of the Year during their shock Premier League title triumph in 2016.
"Riyad is a hugely talented player," Begiristain told the official Man City website. "He beats defenders and creates space.
"Over the past few years, he has established himself as one of the Premier League's most exciting players.
"We're sure he will bring additional attacking quality to our squad."
Mahrez is Man City's first major signing of the summer following a season in which Pep Guardiola's side broke several records en route to the Premier League title.