Mendez, who posted a game-high 23 points on top of six rebounds and five steals, became the league's sixth member to reach the 2,000-point plateau, while Chiang joined the 1,000-point club as its 39th member.
Mendez and Chiang, however, couldn't celebrate completely as Class '83 played a kill joy's role in gatecrashing their party.
Stephen Tan tossed in nine of his 15 points in the first period to power Class '83 to a blistering 22-8 start.
Class '83 toned down offensively in the succeeding period, but got back to work in the third quarter to preserve a 13-point advantage, 53-40, going into the final 10 minutes of the contest. The Chester Enterprises-backed squad never looked back from thereon.
Tan also had 13 rebounds, two steals and two blocks although it was Edwin Lim who topped Class '83 with a season-high 18 points, four assists and three caroms. Cesar Ting added 14 points and six rebounds, while Christopher Cokaliong chipped in 13 markers and eight rebounds as they improved to 6-2.
Chiang finished with 12 points, five rebouds, four assists and two steals, while Ryan Yap donated 10 markers and six rebounds for Class '89, which fell to 2-6.
In the other game, Kent Benedict Uy netted in a career-high 38 points as Sun Gold 2005 prevailed over JV Shop N' Shop '97 in overtime, 78-75. Uy also had seven rebounds, two assists and two steals in his finest game of the season, so far.
Philip John Lua scored 18 followed by Godsent Alegado with 17 points and six rebounds for Class 2005, which notched its only second victory in seven starts.
Bryan Labus fired a season-best 21 points and nine rebounds, while Aubrey Jones Ibones dished out double-double show of 13 points and 11 rebounds but their efforts went for naught as Class '97 suffered its fourth defeat against only two wins.
The scores
First game
Class '83 (67) - E. Lim 18, Tan 15, Ting 14, Cokaliong 13, R. Yu 4, Yao 2, Co 1
Class '89 (62) - Mendez 23, Chiang 12, Yap 10, Chua 7, Lao 4, Mirhan 4, Ong 2
Second game
Class 2005 (78) - K. Uy 38, Lua 18, Alegado 17, Angcay 5
Class '97 (75) - Labus 21, Ibones 13, Dano 10, Maurin 9, T. Tan 8, Uy 4, Sy 3, Tan 3, Maderazo 2, Chan 2