RIVERSIDE — In preparing for its CIF Southern Section Division V quarterfinal match, the Flintridge Prep boys' water polo team figured it had every nugget of information covered concerning Riverside Poly.

The Rebels, looking to advance to the semifinals for the first time in the program's history, learned about some of the schemes that the Bears tend to run on offense and that they're well-conditioned. What the Rebels didn't have was any information on utility player/driver Robert Bentley.

It caught the fourth-seeded Rebels off guard, as Bentley finished with a career-high 11 goals Saturday afternoon to lead host Riverside Poly to a 17-9 win at Bobby Bonds Park's Sippy Woodhead Pool.

"We didn't know anything about him and we didn't have an answer for him," said Flintridge Prep third-year Coach Dan Hare, whose team finished 17-9. "We learned what we could about them, but he did a lot of things well.

"They kept giving him the ball and you might as well ride a guy that's hot like that."

Riverside Poly, which won the Inland Valley League championship, will next meet top-seeded Glendale in a semifinal match at 7:30 p.m. Wednesday at Mount San Antonio College in Walnut. The Bears, who improved to 20-11, are in their first year in Division V after previously competing in Division II.

Flintridge Prep, which placed second in the Prep League before beginning the playoffs Wednesday with a win against Whittier, stayed close with Riverside Poly through the first half. The Bears owned a 7-5 halftime advantage before taking charge in the second half.

Riverside Poly, which posted an opening-round home playoff victory against Burroughs on Wednesday, scored six third-quarter goals to build a 13-8 lead. Bentley had four goals in the third quarter for the Bears, who have scored 18 second-half goals in their two playoff matches.

'We have kind of a young team this year, but we are conditioned," Riverside Poly Coach Mike Cardey said. "[Bentley] is a smart player, and he knows how to feed it and shoot."

Bentley scored three goals in a row in less than three minutes late in the third quarter to make it 13-8.

Flintridge Prep had a bevy of golden scoring opportunities throughout the match. The Rebels converted on just two of seven man-advantage chances and didn't capitalize on a rare two-man advantage in the last 30 seconds of the first quarter while trailing, 3-2.

"We had some great chances to score, but couldn't convert on them," Hare said. "You'd like to think that some of those would have resulted in goals for us.

"The third quarter was the difference. We got a little too passive on defense and it cost us at times."

Diego Delgado, who finished with a team-best four goals, gave the Rebels a 2-1 lead with 4:19 left in the first quarter. Mark Torres of Riverside Poly tied it at 2 with 3:34 left in the opening quarter. Bentley then scored to make it 3-2 with 2:32 left before scoring a goal just as the buzzer sounded to end the quarter to extend the lead to 4-2.

Delgado knotted it at 5 on a five-meter goal with 5:08 left in the second quarter, but Bentley gave the Bears a 6-5 advantage with 3:07 remaining. The Bears' Jonah Saenz capped the first-half scoring with a five-meter goal with 30 seconds remaining.

Delgado said the Rebels couldn't get on track in the second half.

"We didn't play good defense, especially in the third quarter," Delgado said. "We didn't play up to our potential in the second half.

"I thought we had a great year. We did better than a lot of people thought we would."

Flintridge Prep got two goals apiece from Ethan Vandeventer and Jamie Walker and one from John Treinen, who joined the Rebels near the midway point of the regular season after transferring from Loyola.

Saenz finished with a pair of goals for the Bears, who also got one each from Joey Dempsey, Zach Ritter and Bradley Tormey.

Hare said the Rebels can learn from what they accomplished and apply it toward next season.

"We have virtually our entire team coming back," Hare said. "We feel like we will be back next year and try to go further."

charles.rich@latimes.com