Old impressions die hard. And for many, perhaps, it took cornerback Eric Warfield’s interception just before halftime Sunday to dispel the impression of him as a chronic underachiever. He’s on his way to his best season ever and any team in the league would love to have him.

Warfield’s next interception this season would ruin a neat bit of symmetry. He now has four interceptions in each of four straight seasons. His latest interception set up a touchdown for a 35-3 lead in the Chiefs’ 56-10 rout of the Atlanta Falcons.

No Chiefs player has been knocked more often than Warfield over the past few years. The physical skills to become one of the league’s better cornerbacks have always been there. But the consistency has not.

In one sense, however, Warfield’s been misunderstood. Or, more accurately, the nature of his position has been misunderstood.

Cornerback is widely perceived as a skill position that requires exceptional speed but little experience. So cornerbacks who struggle early in their careers tend to get written off. Fact is, cornerbacks routinely need several years to mature, and a smart veteran can stick around long after his best 40-yard dash time becomes a distant memory.

Cornerbacks need to study hard and acquire savvy because few can win a one-on-one battle based upon pure physical abilities. A cornerback usually faces a wide receiver who’s just as fast or faster and often bigger. The receiver’s running forward and the cornerback’s often backpedaling. The receiver knows where he’s going. The cornerback doesn’t. The receiver almost always sees the ball coming. The cornerback may not.

The bottom line is that a cornerback is asked to routinely shut down often-superior athletes who are holding all the cards. That’s why cornerbacks earn their money and the good ones earn it for a long, long time.

Deion Sanders is hardly the youngster who wowed NFL scouts with a blazing 40-yard dash at the scouting combine in 1989. But at age 37, and playing his first season since 2000, he picked off two passes Sunday in a 20-6 victory over the Buffalo Bills. He returned one interception 48 yards for a touchdown.

Sanders, of course, was a top five draft pick who made the Pro Bowl in his third season. Sanders and such cornerbacks as the Denver Broncos’ Champ Bailey came into the league with so much talent that they could make immediate impacts.

They’re the rare ones. When I see a talented young cornerback roasted, I think of cornerbacks like Terrell Buckley and Otis Smith — who were burned, maligned and written off but kept their jobs in the NFL for more than a decade.

Buckley, the fifth overall pick of the Green Bay Packers in 1992, was considered an irredeemable bust and traded to the Miami Dolphins before the 1995 season. Buckley’s legion of critics included TV analyst Jimmy Johnson, who suddenly changed his tune when he took over the Dolphins a year later. Buckley became a solid starter and is spending his 13th season as a New York Jet.

Smith, an undrafted free agent out of Missouri, wasn’t blessed with blazing speed and seemed to get beaten much too often to survive in the NFL. And he bounced around for much of his career. But when all was said and done, he spent 13 seasons with four teams and started in two Super Bowls. Smith was 38 when he was cut for the last time.

Warfield, 28, and in his seventh season, is a relative pup. If he sustains his current level of play and overcomes his off-the-field immaturity, he’ll be a Pro Bowler. As the Chiefs continue reconstructing their defense, he should qualify as one of the cornerstones.