D.C. United didn't waste any time at Maryland SoccerPlex on Wednesday night -- in either half.

United scored less than 45 seconds into the first half and barely 75 seconds into the second to earn a berth in the U.S. Open Cup semifinals for the third consecutive season with a 2-0 win over the Harrisburg City Islanders.

The victory gave D.C. United a much-needed confidence boost and set up a showdown with Columbus at RFK Stadium on Sept. 1.

Branko Boskovic opened his scoring account in his first start for D.C. United thanks to a mistake by the Islanders. Center back Jerritt Thayer misplayed Devon McTavish's through ball down the left side. Santino Quaranta waltzed in and centered to Boskovic for an easy finish from the penalty spot and an immediate lead.

"It's good for the whole team, I think, the confidence and everything for the next game," said the Montenegrin playmaker, who deferred credit on his goal. "Tino gave me good ball, and I only put in goal. He do most of job."

United doubled its advantage just after halftime when Bill Hamid's long clearance landed at the feet of Boyzzz Khumalo. The winger fooled Harrisburg goalkeeper Danny Cepero -- who famously in 2008 became the first goalkeeper ever to score in Major League Soccer with New York -- with a cross that somehow found the bottom of the net.

"In the first minute of the game, we matched their intensity," United defender Carey Talley said. "We were getting in behind, and we were running past them, and we wanted to get this game over with early because the longer these games go with these lower-division teams, the tougher they get, and they usually don't go the MLS team's way."

The early strikes allowed D.C. United to settle in and dominate possession for long stretches in each half, but J.T. Noone nearly equalized for the third-tier club in the 26th minute with a volley that dipped just behind the crossbar.

At the other end, United also was unfortunate not to build on its lead when Barry Rice's diving header skipped wide in the 43rd minute.

Cepero made key second-half saves on headers by D.C. forwards Pablo Hernandez and Danny Allsopp and parried away a booming 25-yard strike from Quaranta. He was also saved by the crossbar, which deflected away McTavish's 83rd-minute shot.

"Our whole goal going into this game was to make sure we had the right approach," United coach Curt Onalfo said. "I thought we started both halves very well. I thought at times we played some very good soccer, moved the ball well and created some good scoring chances. It's a good result to get ourselves into the semifinals of the U.S. Open Cup."