City quickly bounced back from their dramatic midweek defeat to Real Madrid in the Champions League, comfortably defeating Newcastle, who are also fighting for a European spot.
Marmoush's hat-trick, which arrived in just 13 minutes, marked a memorable debut for him, while academy product James McAtee added a late second-half goal to seal the convincing win.
Guardiola was thrilled with Marmoush's contribution, emphasizing his belief that the goals would come for the ã59 million signing:
"The way we played, we remembered what we were and what we have not been this season," Guardiola said. "Marmoush did really well in Germany, a player with his quality and pace, I was pleased with the way he scored. Against Orient he missed chances, but today in the final third he was really good.
"We knew sooner or later he would score goals, he is a good finisher. Of course he has to improve, but now we see how he handles the compliments."
Guardiola also praised his other January acquisitions, Nico Gonzalez and Abdukodir Khusanov, particularly highlighting the Spanish midfielder's role in the impressive performance.
"We always try, but sometimes we cannot do it. I am really pleased with the pace and intensity we had up front, Nico (Gonzalez) and (Abdukodir) Khusanov were extraordinary. We need to win these games to qualify for the Champions League. We have to make this kind of performance to send our people home happy.
"We were really good, good energy up front. Gonzalez helped us a lot, I was really pleased because we needed him, it has been a tough three months.
"He is our mini Rodri! He has a huge presence, his pace, and his time at Barcelona academy, it is all about the ball and positioning. He has the desire to have success in the Premier League, he is here to prove himself."