The "Eisernen" made a perfect start on home soil as Christopher Lenz tested Mainz goalkeeper Robin Zentner in the early stages, before Max Kruse nodded home his debut goal after Sheraldo Becker's pinpoint cross to the far post in the 13th minute.
Mainz failed to put up any resistance while Union relentlessly tripled their lead after Marvin Friedrich headed home Christopher Trimmel's free-kick in the 63rd minute for 3-0.
China's Shi Yanghe and Zhao Jiangqiong won the men's and the women's 65km races respectively.
The last set became a lop-sided affair for Tianjin, which went on a 12-4 run to pull away and kept the advantage until the end.
The emerging powerhouse tamed Hebei by a 44-point gap on Friday. Center Li Yueru shot 10 of 12 from the field to finish with a game-high 21 points. Chen Liyu helped with 16. Wei Wei nailed 14 points off the bench.
"We played great in the first half, but after bench players came in, they suffered a bit and failed to maintain the level on both ends," said Jiangsu coach Ding Tie.
Wuhan and Jiangsu will vie for the league championship on this Sunday. Enditem
On Friday Heerenveen drew 1-1 at FC Utrecht and Vitesse beat Heracles Almelo 3-0 on Saturday. Feyenoord now leads the Eredivisie with 10 points after four matches. PSV and Heerenveen also have 10 points, but Feyenoord's goal difference is better. Vitesse and Ajax are fourth and fifth with nine points. Enditem
Napoli was banned from traveling by local health authorities, after Piotr Zielinski and Eljif Elmas tested positive for COVID-19.
In the other game on Friday, Shaanxi edged Wuhan 80-78. Enditem
"But I told my players it is the utmost honor to play for the national team," he added.