After many years of trial and error, Nobunaga finally captured Mino in 1567. I think the key to Mino was the Mino Big Three (Ando Morinari, Ujie Bokuzen, and Inaba Yoshimichi) switching over to the Oda. Once that happened, the Saito control of Mino quickly disappeared.
The Shincho-Ko ki's take on Nobunaga's conquest of Mino. This comes from the new English version of The Chronicle of Lord Nobunaga by J.S.A. Elisonas and Jeroen Lamers (p. 114)
"In the first decade of the Forth Month, [Eiroku 9 (1566)], Nobunaga crossed the wide expanse of the Kiso River and deployed his troops at Kagamino in Mino Province. His enemy Saito Tatsuoki had his men sally from Inokuchi and take up positions in the village of Shin Kano. the terrain between the two armies was difficult and unsuited for cavalry action. Nobunaga therefore terminated this operation on the same day.
On the first day of the Eight Month, [Eiroku 10 (1567), the Mino Triumvirs-Inaba Iyo no Kamai [Yoshimichi], Ujie Bokuzen [Naomoto], and Ando Iga no Kami-agreed among themselves to defect to Lord Nobunaga's side and asked him to accept hostages from them. Accordingly, Nobunaga sent Murai Minbu no Jo [Sadakatsu] and Shimada Tokoro no Suke to western Mino to pick up the hostages. But even before these had arrived, Nobunaga suddenly sent his men up Mount Zuiryoji, a spur of Mount Inokuchi. While the Saito were still trying to guess whether these troops were friends or foes, Nobunaga had already set fire to the town, denuding Inokuchi Castle. That day, an extraordinary strong wind blew. The next day, Nobunaga divided the responsibilities for constructing the siege works and had a bamboo palisade put up all around the castle, sealing it off from the outside world. In midst of this, the Mino Triumvirs presented themselves before Nobunaga to pay their respects. They were bemused by all activity. but Nobunaga went about his business in his habitual offhand manner.
On the 15th of the Eight Month, while his garrison surrendered, pleading in various ways for mercy, Tatsuoki escaped in a boat to Nagashima in the Delta, going down an arm of the Kiso River. Nobunaga now commanded the whole of Mino Province. He moved his seat from Mount Komaki in Owari to Mount Inaba in Mino and renamed the castle from Inokuchi to Gifu. One year later, the following took place:"
This was important step to controlling the nation. He controls central Japan, controls Japan. it would only one year later when Nobunaga marches his army into Kyoto. For the Tenka!
Nobunaga no tame!
Tenka no tame!