Bhagavad-Gita 1-4

Atra shoora mahaShwasa bheemarjuna samayudhi

Yuyudhaano viraatascha drupadascha maharathaha ||4||

"There are great courageous warriors who are equivalent to Bheema and Arjuna like Yuyudhana, Virata and Drupada."

Duryodhana knows that Bheema and Arjuna are the key opponents. They are the gold standards against whom he compares all other warriors. And moreover they are at the centre of his thoughts, especially Bheema whim he tried to eliminate since childhood and who turns out to be the terminator of the entire Kauravas and the real hero of Kurukshetra war.

Of all the people, the first name he mentions is that of Yuyudhana. Yuyudhana also known as Satyaki was a great warrior, a close friend and devotee of Lord Krishna and the only Yadava other than Krishna to be on Pandavas side. There is a story both Duryodhana and Arjuna had approached Krishna before the start of the war to woe him on their side. Knowing this Krishna pretended to be sleeping. Duryodhana came first and sat near his head end and then arrived Arjuna who sat near his foot end. It was natural that as soon as Krishna opened his eyes he saw Arjuna and spoke to him. When Arjuna told that he came to ask for his help, Duryodhana immediately told Krishna that he had come first and that Krishna should offer his support to him. But wise Krishna told that when he opened his eyes he first saw Arjuna. He told that they can either choose Lord Krishna or his entire army but the first choice would go to Arjuna as he saw Arjuna first. Duryodhana was overwhelmed with joy when Arjuna chose Lord Krishna because he would get the support of mighty Yadava army. But Satyaki decided for himself that in this Dharmayuddha (Battle for righteousness) he would fight on the side of Pandavas. The pinch that Satyaki, a great warrior, instead of being on his side is on the other side probably made Duryodhana put him first on the list.

Then he mentions Virata. Pandavas hid in his kingdom during Agnaatavasa (the 13^th year after finishing 12 years of vanavasa). Virata is not known to be a powerful king as he was subdued by his brother-in-law Keechaka, who was killed by Bheema. But still Virata is second in the list of Duryodhana probably because he felt that Virata came in his way of identifying the Pandavas during agnatavasa. Had he found them, then the war would have postponed by at least another 13 years as Pandavas had to do their second round of Vanavasa and agnathavasa.

The third name is that of Drupada. Duryodhana was worried if he would get the full support of Drona as all his favourite pupils, especially Arjuna was on the other side. That is why he brings Drupada again and again into picture to remind Dronacharya that it is his personal war too and he cannot falter or change sides at this time.