OAKLAND -- All games are not created equal.

Oakland first baseman Brandon Moss gets it.

And, he said, so do his teammates.

OK, it's late May, and Friday night was one of 162 regular-season games on the A's schedule.

But it was against the Angels. They are an American League West team. They've been hot. They arrived at O.co Coliseum knowing if they could sweep their weekend series with the A's, they could move atop the division.

So much for that idea.

The A's made a series opening statement on Friday night, a 9-5 victory against the Angels. They stunned the Angels with a five-run first, highlighted by Moss' first career grand slam, knocking out Angels starter Garrett Richards after he retired only two of the 10 batters he faced.

Mission accomplished.

"Everyone tries to say a win is just a win and a loss is just a loss, but when you play within our division you have a chance to drastically improve your situation," said Moss. "We saw that last year. We were playing well at the end of August and beginning of September and went into Texas [and swept the series.] By the time the series ended there wasn't a race."

The A's arrived in Texas 3 1/2 games up on the Rangers. They left with a 6 1/2 game edge. They clinched their second AL West title in a row six days later. And the year before? Well, the A's went into the final three games of the season two games back of the division-leading Rangers. And the fact it was the Rangers that the A's swept in that season-ending series meant the A's won the division title that year, too.

Now, it's not like the A's are going to wrap up any division title in the next month or two, but there's still a statement to be made during an Angels' visit in late May.

As disappointing as the Angels have been the last two seasons, they have bounced back from early season struggles this year, rebounding from an 11-13 starts to arrive at O.co Coliseum on Friday afternoon having won 14 of their last 20 games and having not lost any of their last six series.

"We know they are a good club," said Moss. "We know they have talent. Last year and the season before it was a surprise the way they finished. We know they were better than that."

The A's aren't bad themselves. They don't have the payroll or the mega stars like the Angels do with a Mike Trout or Albert Pujols or Sunday's starter Jered Weaver.

They do, however, have a versatile roster that fits together well, and finds a way more often than not to win games.

And they have an ability to grind.

OK, they put that five spot on the board in the first inning on Friday night, but they weren't done. Josh Donaldson -- who had that walk-off, three-run home run against Detroit on Wednesday -- not only led off the second inning with a home run, but delivered a two-run homer in the fifth. In between, Donaldson singled in a run in the third, which allowed the A's to easily withstand an Angels comeback attempt.

The A's may have taken two out of three in Anaheim six weeks ago, but all three games were a one-run decision, and the last two went extra innings.

"We knew this year, once we saw them at their place that their bats are alive," said manager Bob Melvin. "It's why it is nice to take the first game of this series. They can make things happen in a hurry. We're up 7-0 and suddenly they are back in the game. You never relax against that team. The lineup is deep."

What's more the A's had lost six of eight in a warm up for the arrival of the Angels, who cut 2 1/2 games off what had been a four-game deficit. And the losses hadn't been pretty. There were a pair of one-run losses in a four-game split with Detroit earlier in the week. There was that three-game sweep by Toronto last weekend, and there was a 5-2, 11-inning loss at Tampa Bay on May 22 that started the slide.

Not that they were overly concerned. That's not the A's way. They just show up for work each day and try to get the job done.

Mission accomplished on Friday.

"What's great about baseball is it doesn't matter who you are or how much money you are making," said Donaldson. "When you get the opportunity to put a jersey on you have to prove yourself every day.

"Albert Pujols has to prove himself. Mike Trout has to prove himself."

And for more than two years now, it has been the A's who have been proving themselves time and time again in the AL West.