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ENGLEWOOD, Colo. -- **Among tight ends this season, only Antonio Gates is in Julius Thomas' class when it comes to touchdown receptions. But given Gates' body of work in the last dozen seasons, it's only fair to say that Thomas is in Gates' class.

Thomas continues to earn respect, and leads the league with nine touchdown receptions. But Gates, eight years older, has long since banked a boundless stash of credibility -- and is right behind Thomas for scores by tight ends, with seven.

"He's hard to stop," said Broncos safety Rahim Moore. "I don't know one person since I've been in the NFL that's stopped him, literally."

Gates has not carved up defenses since the dawn of time; it only seems that way. Nevertheless, it is difficult to envision the Chargers without their stalwart tight end. His career is so lengthy that the quarterback who threw him his first NFL touchdown pass celebrates his 52nd birthday Thursday. That is Doug Flutie, and the 4-yard scoring toss to Gates on Nov. 9, 2003 was a baby step that began a sprint destined to lead to Canton, Ohio.

Peaks and valleys met Gates along the way. He missed 10 games in the 2010-12 seasons, and his per-catch average and big-play output fell along with the Chargers' team-wide fortunes. Whispers of a decline grew.

But through the undulations of his career, Gates dissected the Broncos. Since he entered the league, no player has more receptions (71), receiving yardage (906) and receiving touchdowns (six) against them than the former Kent State basketball standout.

And as was the case for quarterback Philip Rivers, the arrival of former Broncos offensive coordinator Mike McCoy reinvigorated Gates' career. His 77 receptions last year were his most since 2009, and his 11 receptions of at least 20 yards were the most he logged since 2010.

That surge continued this year. Gates' per-game average is slightly down, but his per-catch average is back above 13 yards for the first time since 2010, and he's become the Chargers' most lethal red-zone threat. With seven touchdowns in as many games this season, he's on pace for a career high.

"He uses his hands well," said Broncos weakside linebacker Brandon Marshall. "He's done a great job in the red zone this year."

All but one of the 2014 scores came after Gates aligned himself in a stand-up position just outside the offensive tackle; the other, a one-yard catch in Oakland 10 days ago, saw him split out wide on third-and-goal and make a quick slant inside safety Usama Young. Five of the touchdowns came against safeties; two were against linebackers -- both in the Week 2 win over Seattle, when the Seahawks tried, and failed, to gain a physical advantage with Malcolm Smith and K.J. Wright, neither of whom matches Gates' 255-pound frame.

Gates remains a physical mismatch, a nightmare for opposing coverage schemes that has no end in sight. He's too big and physical for most defensive backs; he's too fast -- and, often, too big -- for linebackers to cover.

"I don't think he has quite the same speed that he used to have, but he makes up for it in his route-running and his savviness," Marshall said. "We've just got to keep our eyes on him and play good technique."

Add the balletic grace, coordination and concentration he showed on a one-handed touchdown grab against Seattle and a catch of a tipped pass last Sunday against the Chiefs, and you have a 34-year-old weapon whose most efficient days might be right now.

"Well, when you're dealing with the best -- arguably -- of all time, him and Tony Gonzalez, I mean, what more can you say?" said Moore.

And to compete against Gates and the Chargers, you have to gamble. That could mean using a slot cornerback like Bradley Roby, whose tenacity and fearless nature could help him compensate for Gates' 63-pound, five-inch advantage. Marshall and rookie Corey Nelson could also be factors in the Broncos' nickel package, along with Moore and fellow safety T.J. Ward. And the Broncos can generate pressure to force errant throws, but Rivers has made a habit of stepping up away from the rush to find Gates, who needs minimal separation to make the catch.

The same "pick your poison" conundrum that exists for teams facing Thomas now greets the Broncos with Gates on the other side of the line of scrimmage.

"It's kind of like, 'OK, how can you stop Peyton Manning in the red zone,' when we've got the No. 1 red zone offense?" said Moore. "It's kind of hard to say, but at the same time, you've got to compete."