At one point early in Sunday’s game, Philadelphia guard Ish Smith drove to the basket for layups on consecutive possessions. The plays were symptomatic of a first quarter in which the Warriors allowed the 76ers to shoot 57 percent from the field.

Even though the open lanes were clogged later in the game, and the Warriors coasted to another victory, those defensive lapses were striking.

Make no mistake: Steve Kerr has noticed them, too.

Kerr realizes this sounds like nitpicking, with his team bearing down on the best regular season in NBA history. But he’s also aware numbers do not lie, and the numbers show the Warriors slipping on defense recently.

They led the league in “defensive rating” last season, allowing 98.2 points per 100 possessions. Through Sunday they ranked fifth this season, at 100.0 points (the Spurs were No. 1 at 96.0).

More important, the Warriors are allowing 105.2 points per 100 possessions over their past 10 games. That might not sound like a dramatic step backward, but it’s enough to concern the coaches with the playoffs barely more than two weeks away.

“This is perfectly natural during an 82-game season, where things have gone extremely well,” Kerr said Monday. “It’s pretty easy to say, ‘We’ll back off a little bit, we’re still going to win.’ And that’s what’s happened. We are still winning, which — in a weird way — is kind of the problem.

“I think it’s that point of the season where our lead over San Antonio is a little more comfortable and guys are maybe backing off a little bit defensively. But we can’t just expect to turn it on for the playoffs. We’ve got to make sure we stay sharp.”

Kerr did not point to a specific defensive deficiency during this stretch. Rather, he suggested the Warriors can return to their previous form by renewing their focus and raising their intensity.

Scott Strazzante/The Chronicle

Assistant coach Ron Adams, essentially the defensive coordinator, actually was encouraged by the past few games. Before that, Adams said, the Warriors went through a period in which they played “average” defense.

Adams contends the Warriors are a better defensive team than last season, but the numbers don’t reflect it. Why?

“I think we let up in games,” Adams said. “We have a formula for winning, and the guys kind of know they can turn on the switch. From my perspective in defensive basketball, it’s got to be an every-possession mentality. More than anything else, we’ve probably slipped in that area.”

Injuries to Andre Iguodala and Festus Ezeli, two of the team’s best defensive players, no doubt play a role. Iguodala anchors the defense when the Warriors play their small lineup, with rim-protecting center Andrew Bogut on the bench.

Another factor: The Warriors are so off-the-charts dynamic on offense, it’s natural to relax on defense. They lead the NBA in offensive rating this season at 113 points per 100 possessions, after finishing second last season (at 109.7, just behind the Clippers).

Guard Klay Thompson acknowledged the Warriors sometimes rely on their athleticism to bail them out.

“When we’re out there kind of just loafing around, that’s when teams get comfortable against us,” Thompson said. “When we’re switching with some force, and contesting every shot, we’re the best defensive team in the league in my mind.”

That was a big part of the formula in last season’s championship, of course. Playoff games hinge even more on defense, a challenge the Warriors met in steaming to the title.

They have nine regular-season games left to climb out of these defensive doldrums, and then the challenge begins anew.

“I know one thing about the playoffs: You win any way you can, possession by possession,” Adams said. “A lot of the frills from the regular season are thrown out the window.

“I have confidence that when we get everyone healthy, and we get closer to the playoffs, we will again be as we were last year, a team that plays every possession well.”

Ron Kroichick is a San Francisco Chronicle staff writer. Email: rkroichick@sfchronicle.com Twitter: @ronkroichick

Tuesday’s game

Who: Wizards (36-37) at Warriors (66-7)

When: 7:30 p.m.

Where: Oracle Arena

TV/Radio: CSNBA, TNT/680

Things to watch

The Wizards might want to watch Klay Thompson in three-point land. Thompson, in the wake of consecutive 40-point games, was named Western Conference Player of the Week on Monday. He shot 62.2 percent (28-for-45) last week on three-pointers.

The Warriors must win at least seven of their final nine games to break the NBA record for most victories in a season (72). Also relevant: Their magic number for clinching the No. 1 seed in the West is five. They lead San Antonio by 4½ games, with nine left.

Marreese Speights is providing serious scoring punch off the bench. Speights has averaged 10.9 points in his team’s past 11 games, boosting his season average to 7.2. He had 17 points in 20 minutes Sunday against Philadelphia.

Forward Brandon Rush missed part of Monday’s practice to get treatment; he banged knees with another player in Sunday’s game. Head coach Steve Kerr described Rush as “probable” for Tuesday night’s game.

The Wizards need a late surge to sneak into the playoffs. They’re tied with Chicago for ninth place in the East, 2½ games behind No. 8 Detroit.

Stephen Curry went for 51 points when these teams last met, a 134-121 Warriors victory Feb. 3 in Washington. Curry made 11 three-point shots in that game (on 15 attempts). Washington point guard John Wall scored 41.

— Ron Kroichick

66-7

The Warriors need to go at least 7-2 to break the 1995-96 Bulls’ record of 72 wins in a season.