The 25-year-old England international has settled quickly into City's back line and played a key role as Guardiola's side edged a tight contest. It was another composed display from Guehi, who helped City withstand late pressure to claim all three points.
"It's a top club," Guehi said. "Since I came here, everyone has been so welcoming - players and staff. I have had to change my game completely. I am learning every day.
"When to pass the ball, committing players - so many aspects I am learning on the job. It's been great because I have had a lot of help."
He also praised Guardiola's influence on his development.
"How you see Pep on TV is what he is like - passionate, intense and a winner. He wants to play his way. I am just glad I have the opportunity to be here."
City twice took the lead through Nico O'Reilly, who struck in each half, while Lewis Hall's deflected effort briefly brought Newcastle level. The visitors pushed hard after the break, forcing City to defend deep during a demanding second half.
Guehi was central to that resistance, organising the line and dealing calmly with Newcastle's physical threat.
"These games are always difficult - always tough to play in," he said. "Newcastle show intensity, endeavour and quality - it's a really good win.
"Maybe not a statement win but one which puts us in a good position."
City's attention now turns to Wednesday's home fixture against Nottingham Forest, as Guardiola's side look to build momentum in the title race.