It's the simplest of instructions, and at halftime the Union clearly got the message: Shoot the ball!

After being outshot 14-1 and outscored 1-0 in the first half, the Union were an entirely different team in the final 45 minutes Wednesday night.

The aggressive approach led to a 2-1 victory over the New York Red Bulls in a round of 16 game in the Lamar Hunt U.S. Open Cup at Talen Energy Stadium.

The Union, who have lost in the previous two U.S. Open Cup finals, advanced to the July 20 quarterfinals against the host New England Revolution.

"We knew the first half wasn't us," said Chris Pontius, who scored both Union goals. "The way we dominated the second half and took over the game, that is what we are about."

In the second half, the Union outshot the Red Bulls, 7-3.

"The players responded well in the second half, we pushed the tempo of the game," Union coach Jim Curtin said.

Both Union goals came from the combination of Ilsinho to Pontius.

In the 55th minute, the Union scored the equalizer when Ilsinho's sent Pontius on goal. Pontius took one dribble and from 16 yards out chipped a shot past sliding keeper Ryan Meara.

Then in the 60th minute, Ilsinho sent a chip from the right side toward the far post, where Pontius one-timed it in from close range.

"Ilsinho put it right on my foot and I put it away," Pontius said.

The Union used their regular lineup minus their two top forwards because of injury. C.J. Sapong hasn't played since suffering an ankle injury on June 1. Curtin said Sapong will be a factor in Saturday's Major League Soccer game at Houston.

Sampong's replacement, rookie Fabian Habers, was out because of a hamstring injury that has him listed as day to day.

Sebastien Le Toux, who frequently played up top in his earlier tenure with the Union, started as the lone forward. Le Toux left the game in the 79th minute after hitting his head in a collision.

Near the end of the contest in separate incidents, Union assistant Mike Sorber and Red Bulls head coach Jesse Marsch were thrown out of the game.

The Red Bulls used most of their regulars with the exception of keeper Luis Robles, who has started 123 consecutive Major League Soccer games and was getting a breather.

In the second minute, Union defender Richie Marquez saved a potential goal by blocking a rebound in front from the always dangerous Bradley Wright-Phillips.

Marquez wasn't so fortunate in the 17th minute.

He failed to clear a Red Bulls free kick that went to midfielder Mike Grella, whose blast from inside the box opened the scoring.

Union keeper Andre Blake made several diving saves on shots from distance in the first half, keeping his team in the game.

He and the Union were fortunate in first-half stoppage time when Wright-Phillips chipped a shot past a diving Blake but over the goal.

The Union's approach and fortunes changed dramatically in the second half.

mnarducci@phillynews.com

@sjnard