Wang saw Li Shimin's troop movement, but not sure what Li Shimin was intending to do, took no action. Li Shimin's forces quickly engaged some of Dou's forward forces, and Tang forces initially prevailed. Li Shimin then wrote to Dou, trying to persuade him to end his attempt to save Wang, but Dou persisted and proceeded to Hulao himself. The armies then stalemated at Hulao. Dou's strategist Ling Jing () suggested that instead of heading to Zheng's capital Luoyang, which Li was sieging, that he attack Tang's Fen (汾州, roughly modern Lüliang, Shanxi) and Jin (晉州, roughly modern Linfen, Shanxi) Prefectures and be poised to further attack Tang's capital Chang'an in order to seize Tang territory as well as force Li to give up the siege on Luoyang. However, Wang's emissaries Wang Wan (王琬, Wang Shichong's nephew) and Zhangsun Anshi () persuaded Dou that Luoyang was about to fall and needed his aid immediately, and so Dou headed for Luoyang. When Empress Cao heard this, she tried to persuade Dou to accept Ling's plan, stating: Dou, however, responded: On one day in summer 621, Dou launched an all-out attack on Hulao, but Li Shimin, wanting to wear him out, declined his challenge, and later during the day, after the Xia soldiers had become tired, Li Shimin launched his counterattack. The Xia forces panicked and collapsed. Dou was wounded by a spear, but still fled, but when he reached the Yellow River, intending to cross, he suddenly fell off his horse. The Tang generals Bai Shirang () and Yang Wuwei (), who were chasing him, captured him and took him back to Li Shimin. Li Shimin rebuked him, "I was only attacking Wang Shichong. What have I done to you that you come out of your own realm and to interfere with me?" Dou responded sarcastically, "If I did not come, I would have required you to extend your campaign." Empress Cao and the Xia official Qi Shanshing () fled back to Ming Prefecture. Li Shimin took Dou, Wang Wan, and Zhangsun to Luoyang and displayed them to Wang Shichong. Wang Shichong considered fighting his way out of the siege and fleeing to Xiangyang (襄陽, in modern Xiangfan, Hubei), but his generals pointed out that they needed Dou's support, and now that Dou was captured, there was little else to do. Wang Shichong therefore surrendered Luoyang to Li Shimin. The cities