Army and the XVIII Corps (without its 62nd Army) to stay in Baoji and Tianshui to face nationalist force under Hu Zongnan's command to secure the left flank and the rear of the communist main force, and the 64th Army of the XIX Corps would push toward Guyuan and Haiyuan regions to face nationalist force Ma Hongkui's command to secure the right flank for the communist main force. The communist I Corps and the 62nd Army of the XVIII Corps would push toward Longxi, Lintao, Linxia and Xunhua regions and then cross the Yellow River to attack Xining, thus cutting off the nationalists' escape route from the rear. The communist main force consisted of the II Corps and the XIX Corps without its 64th Army totaling 5 armies near 150,000 troops would push toward Lanzhou from Xi'an via Xi'an-Lanzhou highway in two fronts, the northern front and the southern front. First stage On August 9, 1949, the communist 1st Field Army begun its attack toward Lanzhou and Xining from eastern Gansu. On August 14, 1949, the communist XIX Corps took Dingxi, while on August 16, 1949, the communist II Corps took Yuzhong and the communist I Corps took Lintao, forcing Ma Bufang's nationalist Cavalry Army to flee westward. On August 20, 1949, the communist I Corps took Kangle, threatening Linxia, while the communist II Corps and XIX Corps reached the outskirt of Lanzhou. On August 21, 1949, a total of nine regiments from the communist II Corps and XIX Corps attacked the nationalist stronghold at Southern Mountain outside Lanzhou, but were beaten back with heavy losses after two days of fierce fighting. The communist commander Peng Dehuai decided to call off the attack and regroup so lessons gained in the fighting could be learned and utilized for the following assaults. On August 22, 1949, the communist I Corps took Linxia, completely annihilating Ma Bufang's nationalist Cavalry Army in the process. As the nationalist defenders of Lanzhou were threatened from rear and right flank, Ma Bufang was forced to withdraw the nationalist 8th Cavalry Division and the nationalist 14th Cavalry Division stationed in the northern bank of the Yellow River back to Xining to strength the defense of the provincial capital of Qinghai. The nationalist defense of Lanzhou was further weakened as a result. On August 24, Ma Bufang reported that the Communists were defeated and 10,000 of them were dead.