The Vancouver central defender is slated to play his third game in seven days as the Whitecaps host the Portland Timbers in MLS action Saturday at BC Place.
"I'm looking forward to it, if selected," O'Brien said after practice Friday. "I feel OK. I think the biggest issue has been probably sleeping and preparing for one game and obviously the travelling and trying to recover from that one and get prepared for another one. … I'm enjoying (the run) while it lasts."
O'Brien has helped the Whitecaps go unbeaten this week in MLS and national championship play. Vancouver beat the Los Angeles Galaxy — the league champs the past two years — for the first time ever last weekend.
And he made a number of key plays as the Whitecaps earned a 0-0 road draw with the Montreal Impact on Wednesday in the first leg of their Amway Canadian Championship final.
If the season's trend is any indication, O'Brien will play the entire game once again. The 33-year-old native of Harrogate, England has played all but one minute in 10 MLS games.
Officially, the former English Premier League veteran is credited with 899 minutes. But the total does not take added time into account, so he has actually logged more.
He has also played every minute of three Canadian championship games. No other Whitecap has played as much.
O'Brien's presence will be important again Saturday as the Whitecaps continue to deal with an injury to captain Jay DeMerit (torn Achilles) and depth issues on the back line.
Honduran international Johnny Leveron will watch the game in street clothes after receiving a one-game suspension for a reckless tackle in the win over Los Angeles. Leveron received a yellow card for the infraction, but the league decided it should have been a red.
Defender Carlyle Mitchell, recalled earlier this week from second-tier Edmonton, where he has been playing on loan, will be in the Whitecaps lineup for insurance but is not expected to play.
As a result, O'Brien and the rest of the defenders will be under pressure against a surging Portland squad.
The 3-4-3 Whitecaps are unbeaten at home this season. Vancouver is 3-0-2 in league play at BC Place and also won a Canadian championship semifinal contest against Edmonton on home turf.
The Timbers (4-1-6) are unbeaten in their last nine MLS games. They have also been strong offensively on the road, netting eight goals compared to 10 at home.
The Whitecaps are expected play with a much more offensive style than they did in Montreal, where they deliberately went into a defensive shell. Interim captain Nigel Reo-Coker said they play with more confidence at home.
It will be needed, because Vancouver has never beaten Portland in MLS play. The Timbers hold a 4-0-1 advantage in the all-time series.
"This is an important game in a big week," said Whitecaps coach Martin Rennie. "We identified this week a number of weeks ago, as an important week for the club.
"Now, we just look forward to this game. It'll be a tough game against a team that's doing well and playing with a lot of confidence and enthusiasm. But we are, too."
The game counts as part of an in-season competition, known as the Cascadia Cup, between Vancouver, Portland and the Seattle Sounders, who are also unbeaten against the Whitecaps in MLS play. Brazilian midfielder Camilo said the Whitecaps have to play with the same energy that they displayed in the win against Los Angeles.
"Because we beat L.A., the (defending) champion, we can beat Portland and Seattle, too," he said.
Notes: Will Johnson, a 26-year-old Toronto native, and Ryan Johnson, a 28-year-old from Kingston, Jamaica, share the team lead with four goals apiece. Ryan has a goal and two assists in the last four games while Will has two goals in the past six games. … Whitecaps striker Kenny Miller remains sidelined with a nagging hamstring injury that has lingered for more than a month. Miller has two goals in the three games in which he has played, but he has not seen the pitch since March 30 due to his injury and international duty with Scotland. Rennie expects Miller and midfielder Daigo Kobayashi (ankle) to resume training next week. … Vancouver's Camilo and Portland's Diego Valeri are among four players who are tied for fifth in the league with 13 shots on goal.