Two early goals from Ji Xiang and Cristian Danalache put the visitors in control and that proved enough to earn Jiangsu their third win in four matches despite Hangzhou pulling a goal back through Song Wang's 21st-minute effort.
Second-placed Jiangsu are now four points behind Evergrande, although the pacesetters can restore their seven-point advantage when they face Guangzhou on Sunday.
Third-placed Beijing Guoan were unable to get any closer to the leaders, though, and they are now four points behind Jiangsu after going down 3-1 at Shanghai Shenhua.
The home side took control of proceedings through goals from Song Boxuan (20), Yunding Cao (52) and Pinheiro Moises (75) before Beijing netted a late consolation with Wang Xiaolong's 82nd-minute penalty.
Guizhou Renhe looked set to climb into the top three in place of Beijing as a 43rd-minute Zlatan Muslimovic strike saw them leading 1-0 heading into the dying moments at Liaoning, but the home side salvaged a point thanks to Yang Shanping's 89th-minute equaliser.
Elsewhere, Shandong Luneng beat Changchun Yatai 3-0 with goals from Gilberto (21 and 59) and Wang Yongpo (90) while Tianjin Taida and Qingdao Zhongneng shared a 0-0 draw.
Also, Dalian Shide eased past Dalian Aerbin 3-2, goals from James Chamanga (three and 18) and Martin Kamburov (53) cancelling out efforts from Aerbin duo Yu Dabao (20) and Peter Utaka (57, pen).