TOKYO – For all its complexities, baseball can be a simple game, really.

And it doesn’t get much simpler than the formula the Oakland A’s used Wednesday: Hitch your wagon to a dominating starting pitcher and ride him to victory.

“Sometimes you have to tip your hat to a guy for the way he pitched,” manager Terry Francona said after Rich Harden handcuffed the Red Sox to three hits and a run over six innings and led Oakland to a 5-1 victory and a split of their season-opening series at the Tokyo Dome “Harden made them a very good team tonight.”

Staked to a 4-0 lead after the A’s touched Sox starter Jon Lester for a single run in the second inning and a three-run homer by Opening Day goat Emil Brown in the third, Harden cruised through his six-inning stint, allowing only a mammoth home run by Manny Ramirez (five RBI in two games) in the sixth. He walked three and struck out nine in his 95-pitch outing.

“I want to give [Harden] credit. He pitched a great game,” said Ramirez, who struck out twice against Harden and then again later in the game against former teammate Keith Foulke. “He was tough. I got to give him credit. He pitched great. He had a nasty split. His slider was working. He was [hitting] 95 [on the radar gun]. He’s got it all.”

“Even in hitters’ counts, he threw off-speed, his splitter, and kept us off-balance,” said Francona. “That was a very explosive game. His stuff was phenomenal.”

If the Sox thought that getting Harden out of the game after six was going to open the offensive spigot, they were wrong. They wasted a two-out double by Coco Crisp in the seventh, as Julio Lugo grounded out to end the inning. In the eighth, an error by Bobby Crosby on a sharp one-hopper by Kevin Youkilis with one out gave the Sox — trailing 4-1 at the time — some hope, and Youkilis moved into scoring position on a wild pitch. But Foulke retired David Ortiz (0-for-3 in the game, 0-for-7 in the series) on a flyout to right and then slipped a called third strike on the outside corner past Ramirez.

Oakland added a solo run in the eighth off Bryan Corey. A two-out double by Kurt Suzuki and a single to center from Mike Fiorentino produced a cushion that the A’s wouldn’t need

By that time, Oakland was feasting on the lead it had built against Lester, who, like Daisuke Matsuzaka the night before, struggled with his command and drove up his pitch count early in the game.

“The game changes when you get ahead of hitters,” Lester said. “It doesn’t matter if it’s spring training or the last start of the year. When you get ahead, you can dictate. When you’re behind, they dictate. They can take pitches and swing at what they want.”

“Jon had good stuff. He used all his pitches,” said Francona. “But he worked himself into some deep counts . . . threw a lot of pitches.”

The A’s took a 1-0 lead in the second on a one-out double by Crosby, a two-out walk to Suzuki and a single by former Wheaton College standout Chris Denorfia. Lester limited the damage by catching Travis Buck looking at a called third strike.

“I think what happens to Jon is that he doesn’t always allow himself to get into a groove that his stuff should allow,” he said. “We want him to try to pick up the pace and work quicker. When he does that, he has a lot of good weapons to attack hitters.”

The night got away from Lester, and the Sox, in the third. A leadoff walk to Mark Ellis and a one-out single from Mike Sweeney set the stage for Brown, who ran into an out representing the potential tying run in the ninth inning Tuesday night.

This time, Brown more than made up for his baserunning gaffe, taking Lester out to left with a booming three-run homer.

“I tried to back-door a cutter,” said Lester. “It went down and in and caught too much of the plate. He was looking down and in and he hit it out.”

“He made that one pitch to Brown,” shrugged Francona. “In a game like this, the way Harden was pitching, that was enough.”

Lester then settled down, retiring the side in order in the fourth, but his struggles in the second and third came back to cut his night short. After four, having thrown 83 pitches — just 47 of them strikes — Lester was through.

“It’s disappointing. It’s not the way I wanted to start the year,” said Lester. “But [next week in Oakland], I get another chance with them. Hopefully I can redeem myself and make some adjustments.”

The Sox boarded a bus immediately after the game to take them back to the United States, their trip to Japan complete. But in some ways, said Ramirez, it was no different than a regular-season road trip.

“Anytime you go on the road,” he said, “you’re happy with a split.”

smcadam@projo.com