By Keith Idec

Ratings for HBO’s boxing doubleheader Saturday night seemingly were impacted by direct competition from premium-cable rival Showtime.

HBO’s main event, Sergey Kovalev-Igor Mikhalkin, attracted a peak audience of 674,000 and an average audience of 599,000, according to ratings revealed Tuesday by Nielsen Media Research. The co-feature of HBO’s “World Championship Boxing” offering, Dmitry Bivol-Sullivan Barrera, drew a peak viewership of 570,000 and an average viewership of 512,000.

Showtime’s main event, Deontay Wilder-Luis Ortiz, was watched by a peak audience of roughly 1.2 million and an average audience of approximately 1.1 million.

That made Wilder-Ortiz, which Wilder won by 10th-round knockout, Showtime’s most-watched fight since Wilder’s first victory over Bermane Stiverne. When Wilder won the WBC heavyweight title from Stiverne in January 2015, 1.34 million viewers tuned in, while an average of 1.24 million watched Wilder-Stiverne.

The 38-year-old Ortiz, a previously unbeaten southpaw from Cuba, was commonly considered the most threatening opponent of the heavily scrutinized Wilder’s nine-year pro career.

Wilder-Ortiz began at 10:44 p.m. ET, right around the time Bivol and Barrera were starting the eighth round of their scheduled 12-round fight for Bivol’s WBA light heavyweight title. Kyrgyzstan’s Bivol (13-0, 11 KOs) cracked Cuba’s Barrera (21-2, 14 KOs) with a right hand, dropped him and stopped him in the 12th round.

Wilder (40-0, 39 KOs), who survived severe trouble during the final 40 seconds of the seventh round, knocked out Ortiz (28-1, 24 KOs, 2 NC) at approximately 11:23 p.m. ET. HBO’s main event between Kovalev and Mikhalkin began about two minutes later.

Russia’s Kovalev (32-2-1, 28 KOs) was a 20-1 favorite over his countryman and mostly dominated Mikhalkin accordingly. The WBO light heavyweight champion stopped Mikhalkin (21-2, 9 KOs) in the seventh round.

Showtime’s first fight, Jose Uzcategui-Andre Dirrell, started at 9:36 p.m. ET. Uzcategui stopped Dirrell to win the IBF’s interim super middleweight title following eight mostly one-sided rounds at 10:08 p.m. ET, eight minutes before the Bivol-Barrera bout began.

Viewership for Uzcategui-Dirrell peaked at 807,000. An average audience 673,000 watched that fight.

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.