LOS ANGELES – Shrug off Aaron Cook’s Opening Day struggle in Arizona. It was, after all, Opening Day, and the ball was carrying at Chase Field, as even the Diamondbacks could attest.

Last Sunday against Philadelphia, Cook may not have been Cook at his best, but on a frigid afternoon at Coors Field he was good enough to get a victory if the Rockies late-inning relievers hadn’t been so bad.

Saturday, against the Dodgers?

There’s no way to rationalize the mess.

The only thing keeping it from being a perfect afternoon was Cook, himself.

“Los Angeles in the day time?’’ said Cook. “It’s warm, You get a good sweat. You get good movement. It was as normal as it can get.’’

That is, it was as normal as it can get, except for the results.

For the second time in three starts, Cook’s sinker was missing. The Dodgers made him pay for it in a 9-5  Rockies loss in which only three of the 12 outs that Cook registered came on ground balls.

Heck, Cook even felt good.

“I wish I could put the blame on that, but physically, this is the best I have felt in a long time,’’ he said.

And that, he said, is a concern for Cook in particular, and the Rockies in general.

Cook is considered their ace, but he’s been trumped in all three starts so far this season.

And it is a puzzle. It’s one thing to not command pitches and not throw strikes. But to leave pitches up in the zone? That’s not Cook.

“It’s why this game makes you scratch your head sometimes,’’ said pitching coach Bob Apodaca. “sometimes things you take for granted turn out to be things you can’t control. We’ve got to sit down and determine the problem.’’

The numbers say there are plenty of problems.

Manny Ramirez hit two home runs off him on Saturday, and then Andre Ethier unloaded a three-run shot off Cook that made the score 5-0. Strange? Well, it is only the fifth time in Cooks career he has allowed three home runs in a game. And Ramirez is only the third player to hit two home runs in a game off Cook, the first to do it on the road.

Troy Glaus, then with Arizona, got him twice at Coors Field on Sept. 11, 2005, and on June 11, 2006, Matt Kemp of the Dodgers connected twice at Coors Field.

“His priority every time out is to establish the sinker,’’ said manager Clint Hurdle. “That’s No. 1 on his list. That did not happen (Saturday) and there was no Plan 2 or Plan 3.’’

There doesn’t normally need to be.

In the last four seasons, combined, Cook averaged 2.74 ground ball outs to baseball outs, fifth best in baseball in that stretch. He gave up an average .071 home runs per nine innings, second best ratio in the majors. And he averaged 1.31 grounded-into-double-plays per nine innings, second best in majors.

So far this year?

Well, he has registered 16 ground ball outs and 14 fly balls outs along with six strikeouts and an out on a sacrifice bunt. More concerning is in his 2 1/3 innings on Opening Day he had only two outs thanks to ground balls, and then on Saturday, only three of his 12 outs came on ground balls, and two of those were on the same ground ball, a first-inning double play.

Not only did Manny Ramirez hit two home runs off Cook, but with the Dodgers leading only 2-0, Andre Ethier unloaded a three-run shot that put the Dodgers on top 5-0.

Rare? Only two other times in Cook’s career did he give up two home runs to the same batter in a game and both those games were at Coors Field – Troy Glaus with St. Louis on Sept. 11, 2005, and Matt Kemp with the Dodgers on June 11, 2006. It’s only the 14^th time in his career he’d even given up more than one home run in a game, and the fourth time he had given up three.

“We’ll come back in (on Sunday) and talk about what has happened,’’ said Apodaca. “Right now (after the game) it hurts. You are angry. All the emotions are popping up. It’s the beginning of the season, when you are so optimistic, and this happens.’’

It is a puzzle, but Cook knows there is a solution. He just has to find it.

“I need to keep moving forward,’’ he said. “I don’t want to dwell on it, but I need to look at it and fix it.’’