The former Manchester United, Villarreal, Atletico Madrid and Inter Milan and forward struck in injury-time to mark his first goal since the joining the J.League club from Internacional in January as Cerezo grabbed their first victory of the 2014 ACL season on Matchday 3.
An early opener from Yoichiro Kakitani preceded a brace from Takumi Minamino before Forlan rounded out the resounding win at the Nagai Stadium in Osaka.
Forlan's fellow former Spanish La Liga forward Kalu Uche made it four goals in three Asian appearances when he netted a double for Qatari side Al-Rayyan as they lost 4-3 to Saudi Arabia's Al Shabab in Group A.
The former Espanyol and Almeria attacker, who is loan from El Jaish, scored in the ninth and 41st minutes but could not deny Al Shabab from turning a 3-2 deficit into victory courtesy of a brace from Brazilian midfielder Rafinha early in the second half.
Ex-CSKA Moscow star Vagner Love made it two Group E doubles on the trot by converting twice from the penalty spot as Shandong Luneng skipped away to a two-goal lead before being held to a 2-2 draw by ten-man Pohang Steelers in Korea.
Brazilian striker Love scored twice in last week's 3-1 win at Cerezo Osaka but was unable to influence Shandong to repeat the dose in their third ACL outing.
Former Sunderland striker Asamoah Gyan scored two times for UAE club Al-Ain as they defeated Iran's Tractor Sazi 3-1 in Group C. The Ghanaian now has four goals in three Asian outings this term to go with his tally of 18 in 19 Arabian Gulf League appearances.
Elsewhere, New Zealand international Kosta Barbarouses scored early as A-League club Melbourne Victory edged Yokohama F. Marinos 1-0 to record their first triumph in Group G, as Gao Lin scored a brace in Guangzhou Evergrande's 3-1 win over Jeonbuk Hyundai in Group G's other fixture.
Group A's remaining contest saw Iranian side Esteghlal force a 2-2 draw with UAE's Al-Jazira who were served by an Abdelaziz Barrada brace.
And in Group C, Qatar's Lekhwiya got the better of ten-man Al Ittihad with a 2-0 win thanks to goals from Qatar's Uruguayan-born star Sebastian Soria and South Korea international Nam Tae-hee.
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