Sporting K.C. midfielder Paulo Nagamura, right, gets around D.C. United defender Daniel Woolard during the first half of their MLS soccer match. (Orlin Wagner/AP)

D.C. United made notable strides in almost all areas Friday after several dour performances this spring and was on the verge of sneaking off with a valuable road point Friday night.

But in an excruciating instant, United cracked. A poor pass, a missed tackle, a sharp cross and a poised one-timer by Sporting Kansas City’s Claudio Bieler in the 89th minute resulted in a 1-0 defeat in front of 18,988 spectators.

“It was the best effort to date,” Coach Ben Olsen said. “Unfortunately, we didn’t get anything out of it.”

Despite the improvements, United (1-3-1) remained scoreless in three away matches and fell to 0-5-3 in its last eight visits to Kansas City.

“You have a feeling you should come out with more,” midfielder Chris Pontius said. “Unfortunately, it comes down to one play.”

That one play began innocently enough. Marcos Sanchez had possession near the sideline deep in United’s end and pushed the ball back toward Marcelo Saragosa. Sanchez’s touch was soft, however, and Soony Saad intervened.

Saad, who had entered six minutes earlier, dodged Saragosa’s challenge and crossed to the oncoming Bieler for an eight-yard strike into the lower right corner.

Sporting (3-1-2) then protected the lead without flaw and extended its shutout streak to 429 minutes.

Whether Bieler should have been on the field – and the teams at even strength – was a point of contention for United.

Midway through the first half, Bieler “punched me in the throat,” defender Brandon McDonald said. United pleaded for a red card, but because the incident happened away from the ball, none of the officials apparently witnessed it.

“If he doesn’t get suspended,” McDonald added, “Kansas City turned into the Lakers,” implying MLS would give star treatment to Sporting.

“He clearly hit him,” United goalkeeper Bill Hamid said.

McDonald was treated for several minutes but remained in the match. He and Dejan Jakovic formed a sound partnership in central defense and conceded few opportunities.

In possession, United moved the ball as well as it has all season – even without injured starters Dwayne De Rosario and Nick DeLeon.

However, Lionard Pajoy failed to convert two wonderful scoring opportunities in the first half. In the sixth minute, he one-timed Chris Korb’s deflected cross on target, but Jimmy Nielsen made a kick save.

Sporting’s first quality bid came in the 18th minute when Bieler headed Matt Besler’s long throw-in narrowly wide.

Just before the break, Pajoy used clever footwork and a cutback to beat two defenders, but drove his near-post bid wide from a mere seven yards.

“He had a good night,” Olsen said, “but we’re still looking for more quality in front of the goal.”

Kansas City set the terms after the break, ramping up pressure and serving dangerous balls into the box. Graham Zusi, a U.S. national team regular from the University of Maryland, surged into space in the 70th minute but ripped a 25-yard bid well over the crossbar.

Nielsen stopped a bicycle kick by substitute Carlos Ruiz in the 81st minute, United’s last chance to break the deadlock.

United seemed safely on its way to a tie when Sanchez’s mistake led to Bieler’s goal.

“It’s just a heartbreaking loss,” Jakovic said. “There were definitely stretches where we played well and kept the ball. This one stings.”

United notes: Midfielder Lewis Neal (groin injury) will miss two months, General Manager Dave Kasper said. DeLeon (hamstring) is out another month and midfielder John Thorrington (knee) another six weeks. . . . United will host the New York Red Bulls next Saturday night.