Boston third baseman Mike Lowell gets knocked down while applying the tag to Oakland’s Mike Piazza on a grounder hit by the Athletics’ Bobby Crosby. Piazza, who was out, was injured on the play and left the game.

Providence Journal photo / Bob Breidenbach

BOSTON — In his second season with the Red Sox, Josh Beckett is now breathing rarified air.

In running his record to 6-0 last night with a 6-4 win over the Oakland A’s, Beckett continues to join some pretty select company. He’s the first Red Sox pitcher to start a season 6-0 since Roger Clemens began that way in 1991.

Previously, he was just the third Red Sox pitcher to win five starts in April, joining Babe Ruth and Pedro Martinez.

The Babe, Rocket and Pedro — that represents an exclusive list.

“It’s an honor (to be mentioned with them),” said a humbled Beckett, although his perfect start doesn’t suggest that he belongs on a short list with three of the greatest pitchers in franchise history.

What it does suggest, however, is that Beckett may finally be edging closer to becoming the pitcher the Red Sox were after when they bundled a bunch of prospects for him in November 2005.

Beckett is baseball’s first six-game winner this season, and while that’s no guarantee of season-long greatness, it is a step in the right direction.

To watch Beckett this year is to watch the evolution of a thrower becoming a pitcher.

“He’s got all the talent in the world,” said infielder Alex Cora. “When situations get tough, he’s showing us he’s not the old Josh, letting it go at 97-98 mph and leaving it up in the zone.

Last year, Beckett attacked American League hitters as a Texas gunslinger, determined to challenge them with 95 mph fastballs. That approach worked fine in the National League, where lineups aren’t as deep or dangerous.

But too often, Beckett couldn’t command his breaking pitches and American League hitters — particularly those in New York and Toronto — earned to be patient and sit on his fastball.

When they guessed correctly, they often took him out of the ballpark, connecting for 36 homers, the most allowed by any American League pitcher.

Beckett has kept his mistakes to a minimum this year. In almost 40 innings of work over six starts, he’s allowed exactly one homer.

Credit should go to batterymate Jason Varitek, in whom Beckett seems to have far more trust. Beckett singled out Varitek more than once last night when asked to explain his 6-0 start.

Varitek has apparently gotten Beckett to understand the importance of his secondary pitches and to see the folly of trying to overpower American League lineups.

Beckett was eerily efficient through the first four innings last night, retiring the first 12 hitters Oakland sent up against him.

He was touched for a two-out, two-run single by Jason Kendall in the fifth, then yielded three singles in the sixth for another run. But of the six hits allowed, just one was for extra-bases, eliminating the threat of big innings.

In his seven innings, he walked just one, fanned seven and lowered his ERA to 2.72.

Good starts aren’t new for Beckett. A year ago, he won his first three starts as a member of the Red Sox and posted wins in seven of his first eight decisions.

But in between, he was horribly inconsistent.

Not this year. Beckett has pitched at least six innings in each of his last five starts. In three of those starts, he has pitched at least seven innings.

When the Sox reluctantly parted with Hanley Ramirez, Anibal Sanchez and two other pitching prospects, it was with the hope that Beckett could be the kind of pitcher to anchor a staff for years to come.

Not yet 27, Beckett can remain under the Red Sox’ control through the 2010 season, the twin-centerpiece of a rotation with Daisuke Matsuzaka, with Jon Lester, Clay Buchholz and Michael Bowden filling out the nucleus in the seasons to come.

Better still for the Sox, he was signed to an attractive deal last summer, before the market spiked and sent salaries soaring out of control to the point where Gil Meche landed a five-year, $55-million deal, or $1 million for each of his career wins.

Suddenly, the contract extension looks like a steal, and the trade, while hardly lopsided thanks to Ramirez’s astounding talent, is now, at worst, an equitable swap.

It’s premature to suggest that Beckett has achieved ace status through five weeks. It’s not too early, however, to note that Beckett is improving and once again, resembling the pitcher who willed his overachieving team to a world championship at age 23.

smcadam@projo.com