O'Reilly had two goals and two assists and Buffalo pounded the Edmonton Oilers 6-2 on Sunday night for their first victory of the season.
O'Reilly's four-point effort came alongside new linemate Okposo, a free agent signing who played his first game after missing Buffalo's opener with a sore knee.
"(O'Reilly) might not get as much recognition as he should, but he's such a heady player," said Okposo, who had a goal and an assist in his Sabres debut. "He's such a smart player, you can see it when you play against him and just playing with him, he makes so many little plays, never puts you in a bad spot, he's an easy guy to play with."
O'Reilly said he also felt very comfortable playing with Okposo.
"He's huge, a big reason why we won tonight," he said. "That was my first time getting to play with him, obviously I enjoy it. He does so much out there, he plays such a strong game and to impact the lineup like he did tonight was huge and that's what we need."
Brian Gionta also scored twice, and Matt Moulson had Buffalo's other goal. Robin Lehner made 31 saves.
Benoit Pouliot and Milan Lucic scored for the Oilers, who had won back-to-back games before the loss.
"We looked like the Bad News Bears," Oilers coach Todd McLellan said. "We had guys falling all over the place. We didn't execute. Our passing was poor. From the goaltender to the blue line to the forwards, nobody was ready to play."
Cam Talbot stopped 17 shots for Edmonton. Jonas Gustavsson relieved Talbot in the second period and stopped the only shot he faced before exiting with an injury about 10 minutes later.
Buffalo started the scoring 2:37 into the first period when Sam Reinhart made a nice feed across to Okposo and he beat Talbot for his first as a Sabre.
The Sabres went up 2-0 7:14 in. Okoposo made a great pass while on the power play to O'Reilly at the back door.
Edmonton got one back with 2:40 left in the opening frame when the rebound from Zack Kassian's shot went off the leg of a hard-charging Pouliot and past Lehner.
The Oilers tied the game with 1:00 left in the period when the big rebound from Leon Draisaitl's shot came out to Lucic, who scored his first goal as an Oiler and the 400th point of his career.
Buffalo got a freebie 3:53 into the second when O'Reilly took a shot just from Buffalo's side of center that Talbot badly misjudged and ended up tipping into his own net.
The Sabres restored their two-goal lead midway through the second when Gionta tipped in Johan Larsson's point shot, prompting Edmonton to bring in Gustavsson.
With Talbot back in net, the Sabres made it 5-2 just 37 seconds into the third. Gionta tucked a shot between Talbot's legs on Buffalo's 16th shot of the game.
The Sabres kept it coming with Moulson's power-play goal four minutes later.
NOTES: The Sabres were without a pair of big-name players up front with center Jack Eichel out an expected six to eight weeks with an ankle sprain and forward Evander Kane likely out several weeks with broken ribs. ... Buffalo did get a boost from the return of Okposo, as the free agent signing played his first game after missing their opener with a sore knee. Buffalo defenseman Dmitry Kulikov also made his debut.
Sabres: Travel to Calgary to play Tuesday.
Oilers: Host Carolina on Tuesday.