With Manchester City missing Rodri for the first time since suffering a serious knee injury, this win over eighth-placed Watford in the Championship offers little indication of how they will cope in the long term.

Saturday’s trip to Newcastle should shed more light on Pep Guardiola’s plans and show which experienced player the manager trusts to deputise for the 28-year-old in midfield.

In that game, 19-year-old Nico O’Reilly took the vaunted Spaniard’s No.6 spot in his first competitive match and, although he will not be able to do so against stronger opposition, this fine performance has not hurt his chances of being included in the regular matchday squad.

The City machine was in full swing after five minutes thanks to a merciless finish from Jérémy Doku. After Watford hesitated at the back, James McAtee turned on the left byline and passed to Jack Grealish. The number 10 played the ball diagonally to the Belgian, who skilfully outmaneuvered James Morris and beat Jonathan Bond, the visitors’ goalkeeper.

During pre-season, Guardiola joked about the 6ft 2in O’Reilly’s height, saying it was a change from the more diminutive City academy products Rico Lewis and Oscar Bobb. Rodri is also statuesque and a simple touch from O’Reilly on Lewis at Watford Stadium also brought to mind the injured man with a cuteness that surprised the right-back.

Guardiola will have been pleased with a tackle by O’Reilly on Imrân Louza, which left the number 10 player lying on the ground and inviting City to attack. He was less pleased, however, with an attempted dribble which resulted in the ball being lost, which the coach considers a cardinal sin.

Guardiola made nine changes from the side that drew 2-2 with Arsenal on Sunday. Kaden Braithwaite became the club’s third-youngest debutant at 16 years and 229 days. He was pushed aside by Kwadwo Baah on his way to what appeared to be an equaliser before referee David Webb whistled for a foul. A 50-50 decision that may not have been made outside City’s penalty area, so the youngster got lucky and the Hornets got the opposite.

However, the hack on Phil Foden as he ran onto a pass from Grealish was certainly a violation and the two were standing over the free kick before Foden hammered it into the Watford wall from near the box.

Ten minutes before half-time, Nunes did much better. Lewis, moving inside, played the ball to McAtee, who played it back. The defender tapped it to Matheus Nunes, who felt the yellow shirts dawdling around him, pushed the ball to his left and then overtook Bond on his right from 20 yards out.

Guardiola’s expertly coached side had their opponents where they liked them: on the losing side, exposed to a relentless attack from the Blues. This was the pattern of the first half until Webb blew the whistle for time. But if the unmarked Vakoun Bayo had not missed a simple header moments earlier, the coaches’ team talks would have been very different.

Savinho, whose gentle shuffle and turn inside set up Erling Haaland’s opener against Arsenal, was given the second 45 minutes as Doku was substituted. Combination play with the Brazilian led to a corner, but from that McAtee flicked a pass to Lewis, who didn’t have a proper grip on the ball, and Watford stormed forward, where Nunes sprinted back to deny the danger.

Lewis then passed the ball perfectly to McAtee, who was running into the visitors’ box, but he made a clumsy touch and Bond intercepted it. City were on a roll. Two angled attempts from Foden led to two corners. A laser shot from Savinho bounced off the side netting. On the left, Grealish probed and provoked a rearguard that was as solid as the Gunners in the second half.

Seeing Ruben Dias, Bernardo Silva and Mateo Kovacic warming up was no relief for Tom Cleverley’s men, but the corner they won was. The ball was begging to be put in the net as it fell tantalisingly to Louza’s foot, but his volley was wide.

Seconds later, City were again hot on Watford’s heels when Nunes and Lewis narrowly missed and Tom Ince cleared off Savinho’s line. It was a hectic affair.

A worried Guardiola almost rued those near-misses when Watford countered again and Baah narrowly missed from close to Stefan Ortega’s goal. At the other end, Savinho was closer, hitting Bond’s right post to elicit loud “oohs” from the partially packed crowd.

For O’Reilly, the evening was over. He was replaced by Jacob Wright, and shortly afterwards Braithwaite as well. Josko Gvardiol took his place at left-back.

Grealish hammered the ball into Bond’s chest from close range. The winger should have scored, but despite Ince’s curved long-range shot, it was ineffective.