SAN ANTONIO — The San Antonio Spurs were not going to believe Serge Ibaka was really injured until the Oklahoma City Thunder took the court in the opener of the Western Conference finals without their athletic big man.

Their skepticism was unwarranted.

Ibaka is indeed injured and Oklahoma City needs to find a way to replace his defensive presence.

Tim Duncan had 27 points and the Spurs took advantage of Ibaka’s absence to score more than half their points in the paint, beating the Thunder 122-105 Monday night in the opener of the best-of-seven series.

Tony Parker did not appear limited by a hamstring injury, adding 14 points and 12 assists in 36 minutes in San Antonio’s first victory over Oklahoma City this season.

Ibaka injured his left calf in Oklahoma City’s series clincher against the Los Angeles Clippers.

“He’s not coming back,” Thunder coach Scott Brooks said.