Wu Lei's goal saw Shanghai Port beat Cangzhou Mighty Lions 1-0 and
Wu headed home his 32nd CSL goal of the season in the 14th minute from Oscar's precise corner.
After the critical win, Shanghai Port now have 75 points and have overtaken Shanghai Shenhua, who were held 2-2 at home by Shenzhen Peng City.
Andre Luis put Shenhua ahead in the 47th minute, before Eden Karzev and Matt Orr scored two for the away side in the 70th and 78th minutes.
In stoppage time, Fei Nanduo was knocked down in the box and the referee awarded Shenhua a penalty, which was converted by Cephas Malele.
With the draw, Shenzhen fall into the relegation zone with 26 points after Meizhou Hakka edged Wuhan Three Towns 1-0 to climb up to 27 points.
Elsewhere, bottom side Nantong Zhiyun were condemned to relegation as they lost 3-1 to Beijing Guoan, while Chengdu Rongcheng drew with Qingdao West Coast 1-1 to secure third place in the league.
The CSL title race will be determined next Saturday. Shanghai Port will defend their title if they beat Tianjin Jinmen Tigers at home, while Shanghai Shenhua need to beat Chengdu Rongcheng and hope their city rivals slip up.
