The satellite giant, Virgin, the Competition Commission and the business secretary are all parties in a Competition Appeal Tribunal over the matter.
Sky today began arguing that its 17.9% stake in ITV did not give it "material influence" over the broadcaster's operations.
The government, which ordered Sky to reduce the holding to less than 7.5%, had not proven the need for the change, lawyers for Sky said.
Sky claimed that even if it had chosen to exercise its board voting rights it would not have been able to exert a significant influence.
Arguments that Sky would seek to block ITV investment in free-to-air TV, terrestrial high definition channels, and content, were cited and rejected by Sky.
"Those are not the bases on which Sky went into this transaction," the CAT was told.
The Competition Commission and the Secretary of State will defend their position that "there is likely to be a significant lessening of competition arising from a loss of rivalry in the all-TV market between ITV and BSkyB", and that the proposed resolution is necessary and proportionate.
Virgin Media, meanwhile, will also argue against the Commission and the minister. The company says a reduction of Sky's stake to 7.5% is not sufficient to protect competition.
The tribunal hearing is expected to continue until at least Thursday.