Newport Harbor High's Christina O'Beck (2) scored three goals in the Sailors' win over Los Alamitos on Wednesday. (KEVIN CHANG, Daily Pilot / February 6, 2013)

NEWPORT BEACH — The low shot from Los Alamitos High senior Stephanie Mutafyan came in at lightning speed, forcing Newport Harbor junior goalkeeper Cleo Harrington to react quickly.

It was a reaction that stunned Los Alamitos girls' water polo coach Dave Carlson in the third quarter Wednesday night. Harrington somehow dropped her hands in time to stuff the shot from about five meters.

Another junior also would step up in the showdown for the Sunset League title.

Christina O'Beck led all players with three goals as the Sailors held on for a 7-5 victory over the Griffins at Newport Harbor High.

Newport Harbor (20-6, 5-0 in league) wins the league title outright. It's the Sailors' sixth Sunset League crown in seven years since joining the league in 2006-07.

As importantly, Coach Bill Barnett believes his Sailors will be the No. 4 seed in the CIF Southern Section Division 1 playoffs, and potentially face Laguna Beach in a quarterfinal match. Los Alamitos, which cannot be in the same half of the bracket as Newport Harbor, per CIF rules, likely will drop to the No. 6 spot and have to face Corona del Mar in the quarterfinals.

"I'm so happy that we won," O'Beck said. "It's so important in so many ways — league champions, better seed for CIF. We didn't want to play CdM in the quarterfinals. It just all came down to this game, and I feel like we all knew that. We were nervous, but we were excited."

Another playoff scenario has Newport Harbor seeded No. 3, with CdM at No. 4. The teams are 2-2 against each other this season.

Playoff brackets will be released Sunday at 9 a.m.

Harrington made eight of her 13 saves in the second half, including the aforementioned stop against the Cal-bound Mutafyan, who had two goals and three steals. Harrington helped stop any hope of a rally by Los Alamitos (21-6, 4-1).

After the first meeting of the season between the two league rivals, Carlson said he is certainly a believer in Harrington.

"We had three shots tonight that were incredible shots, that when the ball left my girl's hand I believed it was a goal," Carlson said. "I was blown away that the ball didn't go into the back of the net. And those are just ones that were absolute goals. She made about five or six incredible saves.

"The thing I noticed about her is that she seems to play her best in the biggest games."

Harrington stopped six shots in the third quarter alone, after the Sailors had used four successive goals — two from O'Beck, one from senior Carolyn Smith and one from senior co-captain Elissia Schilling — to open up a 5-2 halftime advantage.

The second goal from O'Beck, 14 seconds before halftime, came as she held position at set. She took the entry pass from senior Avery Peterson and scored.

"I'm supposed to be a set player, but Elissia just dominates," O'Beck said. "I knew that they were going to match up Stephanie with Elissia, so I knew I had to step up into that role since I practice it in practice. 'Coach B' was really happy ... I did his sort of move and it worked. I should probably start listening to him more."

Barnett was happy that she did.

"O'Beck came through," Barnett said. "[Los Alamitos] doesn't have a lot of big girls. If you can get a big girl in at set, and she puts in the effort, you should be able to get a goal. We've been working with her to get up and use her strength. She's a big, strong girl."

The Sailors' game was crisp Wednesday, as they converted four of five power-play situations. Los Alamitos, which had junior Becca Corb foul out early in the fourth quarter, converted two of five on extra.

Senior co-captain Carly Christian also scored twice for the hosts. Her second goal, on a six-on-five, gave the Sailors a 6-3 advantage with 5:36 left. Los Alamitos junior Ella Weber scored from the perimeter to cut her team's deficit, but then O'Beck scored on Newport Harbor's next possession.

Weber added a six-on-five strike with 2:13 left, but the Griffins couldn't get closer. Peterson added a big defensive play on Los Alamitos' next possession, forcing a ball-under turnover to shut down a counterattack.

"We were prepared," O'Beck said. "We've been devoting practice to this game for three weeks."

matthew.szabo@latimes.com

Twitter: @mjszabo