The Citizens won the Premier League title in style last season after Manchester City finished 19 points ahead of their closest rivals, Manchester United.
The Eastlands outfit have made a positive start to the current Premier League season as the Citizens look to retain their top-flight crown for the first time.
Guardiola took over the reins of Manchester City following his stint in charge of Bayern Munich, having turned down the chance to replace Sir Alex Ferguson at Old Trafford in 2013.
Mourinho is currently in charge of the Red Devils as the Portuguese head coach looks to become the first manager to steer Manchester United to title glory since Ferguson.
The 54-year-old has a rich pedigree in the competition after he led Chelsea FC to three Premier League titles during two different spells in charge of the west London side.
Mourinho has also won top-flight titles with FC Porto, Inter Milan and Real Madrid, while he got his hands on the Champions League crown with the Portuguese and Italian clubs.
Asked who has been more influential in the Premier League ahead of Sunday’s Manchester derby, Merson explained why Guardiola has work to do to overhaul Mourinho.
“Pep’s only just started out in this league. He’s spent a bundle of money and gone crash, bang, wallop,” Merson told Sky Sports.
“In his first season, City didn’t do anything then he spent big money on a couple of full-backs and he’s built a team in the way that he wants to play. They’re now irresistible.
“But what Mourinho did at Chelsea was outstanding. Would Pep have won the Champions League with Porto and Inter Milan? I’m not sure. “They are both great managers but when Pep wins three Premier League titles then we can then start putting him alongside Mourinho.”
Mourinho replaced Louis van Gaal at Manchester United in May 2016 after Chelsea FC sacked their legendary manager in December 2016.
He led Manchester United to glory in the League Cup and the Europa League in his first season in charge.
However, Mourinho ended his second season in charge without a trophy to heap pressure on the ex-Chelsea boss.
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