The win at Seoul World Cup Stadium was Gamba's second in two games and put them in control of Group F after Akira Nishino's side kicked off their campaign last week with a win over China's Shandong Luneng.

Leandro claimed all three of his goals in the second half as Gamba won their fourth game in a row in all competitions, following on from a pair of victories in the new J.League season.

Gamba took the lead after just 13 minutes when Masato Yamazaki silenced the home crowd with a fine effort from the edge of the penalty area.

The Japanese side held onto their advantage until half-time, only for Jung Jo-gook to equalise nine minutes after the break when Lee Chung-yung rolled the ball through a crowded penalty area and Jung was left with an easy finish.

Seoul, who dominated proceedings after the restart, were now in the ascendancy and looked the more likely to take the three points.

However, on the hour mark Gamba reclaimed the lead due to some slack defending by the home side. Yasuhito Endo's corner found Leandro unmarked at the far post and he made no mistake.

With 16 minutes remaining Leandro doubled Gamba's advantage when he slotted home from close range following Cho Jae-jin's smart backheel.

Nine minutes later Leandro struck again, completing his hat-trick and sealing a fine win for Gamba with Lee Sang-hyub's 90th-minute goal scant consolation.