The Italy international moved to the Chinese Super League champions earlier this month, after spending much of his career in his homeland, but he took no time to adapt to football in Asia.
His debut did not get off to the ideal start, with Pablo Contreras and Leigh Broxham handing the Australian side into a two-goal lead at the break.
However, after Huang Bowen had pulled a goal back, Diamanti registered his first for his new club to level after 65 minutes before Elkeson continued his goalscoring form from last season to put the hosts ahead.
After that flurry of goals looked to have guaranteed Guangzhou the points, Diamanti completed his brace five minutes from time to cap a superb performance.
Marcello Lippi's men sit level on points with Jeonbuk Motors in Group G after the South Korean side put three past Yokohama F Marinos without reply.
The scores were level after an hour at the Jeonju World Cup Stadium but Lee Seung-ki hit a brace within nine minutes before Leonardo added a third from the spot 19 minutes from time.
Jeonbuk's K-League rivals Ulsan Hyundai also secured a comfortable three points - recovering from an early Brendon Santalab goal to beat Australia's Western Sydney Wanderers move top as the early leaders of Group H.
Santalab scored after just a minute but efforts from Kim Shin-wook, Ko Chang-hyeon and Kang Min-soo ensured Ulsan of three points before Kawasaki Frontale followed suit with a 1-0 win over Guizhou Renhe, courtesy of Renatinho's 31st-minute goal.
"The turning point of the game came when we had to replace (striker Zlatan) Muslimovic because of injury, which changed the atmosphere of the game," Renhe coach Gong Lei explained.
Despite seeing Ali Karimi sent off after an hour, Tractorsazi Tabriz recorded a 1-0 victory over two-time winners Al Ittihad, while Asamoah Gyan was the hero for Al Ain in their 2-1 win over Lekhwiya of Qatar.
Two late goals from Nadir Belhadj and Rodrigo Tabata helped Al Sadd overcome Sepahan 3-1 before the final game of the day saw Al Hilal and Al Ahli play out an entertaining 2-2 draw.
After Luis Jimenez and Grafite had given the visitors the lead at the King Fahd International Stadium, a Nasser Al-Shamrani double gained Al Hilal what had looked at one stage like an unlikely point in Group D.
