Beijing Guoan's winning start to the Chinese Super League was brought to an end on Sunday by defending champions Shanghai SIPG, who reduced the gap at the top of the standings to two points with a 2-1 win over the leaders.
Midfielder Cai Huikang headed home 12 minutes from time to earn Vitor Pereira's side victory as Beijing lost for the first time in the 11 games since the start of the season.
Former Chelsea star Oscar had given SIPG the lead when he sidestepped the defence to score 28 minutes into the game, but Yu Dabao's header had pulled Beijing level just before the hour mark only for Cai to give his side the win.
"Everyone will be disappointed but we have to learn from this situation," said Beijing coach Roger Schmidt.
"We never thought we would go through the entire season unbeaten. It has not been easy for our players to win over the last 10 games.
"It is very difficult to win the Chinese Super League and today the players did not let me down. They were always trying to find a way to level the scores when we were behind."
Beijing's defeat means seven-time champions Guangzhou Evergrande also closed the gap at the top as the battle for the title shapes into a three-way fight.
China international Wei Shihao struck to allow Fabio Cannavaro's side to pick up a 1-0 win against Shenzhen FC that moves them to within five points of the top and keeps them five ahead of fourth-placed Shandong Luneng.
Shandong had goals from Marouane Fellaini, Gil and Hao Junmin to thank for their 3-1 over Guangzhou R&F, taking them clear of Jiangsu Suning who slipped to a 3-2 defeat against Hebei CFFC. Chongqing Lifan were held 0-0 by Henan Jianye.
Former Napoli midfielder Marek Hamsik scored his first goal since moving to China as Dalian Yifang claimed their second win in a row, beating struggling Shanghai Shenhua 1-0 and leaving Quique Sanchez Flores' side just above the relegation zone.
Beijing Renhe moved off the bottom after Makhete Diop put his side ahead before an own goal by Zheng Kaimou ensured they were able to pick up a 2-1 win over Tianjin Teda. Tianjin Tianhai, meanwhile, dropped into 16th and last place following their 2-1 loss against Wuhan Zall.