Henry, back at full strength after a knee injury, opened the scoring in the 29th minute, and Olave scored in the 36th to help New York (2-3-2) win for the first time in its last five tries at RFK Stadium.
United dropped to 1-4-1. The Washington club has scored only two goals and been shutout four times. It has lost two straight at home after a 17-game unbeaten run.
On the opening goal, Dax McCarty created space, and found Henry outside the box. The Frenchman faked to his right, cut back left, came back to his right and slotted a perfect ball into the bottom right corner. United goalie Bill Hamid dove to his left but it was too late.
New York had four corner kicks in the first half, using the third to double the lead.
Taking a short corner, Juninho played the ball to Henry. Henry sent the ball right back to Juninho, who whipped in a shot that was redirected first by Brandon Barklage before Olave slotted it past Hamid into the back of the net. It was the defender's third goal of the season and second in two games.
FC DALLAS 1, GALAXY 0
FRISCO, Texas (AP) — George John scored in the 87th minute to lift FC Dallas past Los Angeles.
John directed a header into the left corner from less than 5 yards, then hit the back of his head on the right post, opening a cut.
Dallas improved to 4-0-0 at home and 5-1-1 overall. Los Angeles dropped to 2-1-2.
In the 69th minute Dallas goalkeeper Raul Fernandez slid a few feet to his left to deflect Landon Donovan's penalty kick. Donovan has scored more career goals against Dallas that any other player with 17.
Donovan made his first MLS start of the season. He took an extended leave of absence following MLS Cup 2012 in December and made his season debut against Toronto FC on March 30 as a second-half substitute.
REVOLUTION 0, SOUNDERS 0, TIE
SEATTLE (AP) — Seattle failed to deliver on coach Sigi Schmid's victory guarantee, tying New England despite dominating most of the play.
In remarks to reporters Friday, Schmid promised that the Sounders (0-3-2), off to the worst start in the five-year history of the franchise, would win for the first time this season.
The Sounders have scored only two goals, and both of those scorers — Eddie Johnson (hamstring) and Brad Evans (calf) — were sidelined with injuries Saturday.
New England (1-2-2) has gone without a goal for four-plus games totalling 388 minutes since scoring in the 62nd minute of a season-opening 1-0 victory at Chicago on March 9.
TORONTO FC 1, UNION 1, TIE
CHESTER, Pa. (AP) — Jack McInerney scored in the second minute of stoppage time to give Philadelphia a tie with Toronto FC.
McInerney, who leads the Union with four goals, scored about 4 minutes after Toronto FC's Ashtone Morgan was ejected with a red card. Morgan accumulated two yellow cards and was sent off in the 88th minute.
Toronto opened the scoring in the 71st minute when Robert Earnshaw scored his fifth goal of the season, tying him for first in the league with the Los Angeles Galaxy's Mike Magee.
The Union is 2-2-2, and Toronto 1-2-3.
REAL SALT LAKE 1, WHITECAPS 1, TIE
VANCOUVER, British Columbia (AP) — Camilo scored on a penalty kick in the 84th minute to help Vancouver tie Real Salt Lake.
Camilo scored after having four shots stopped in the first half as the Whitecaps (2-2-2) earned a point in their first home game since March 9.
Vancouver received the penalty kick after defender Nat Borchers went to field the ball in the box, but accidentally fell and got his hand it.
Second-half substitute Olmes Garcia opened the scoring for Salt Lake (2-3-2) in the 66th minute.
RAPIDS 1, CHIVAS USA 0
CARSON, Calif. (AP) — Rookie Deshorn Brown scored on a penalty kick in the 7th minute and Colorado held on to beat Chivas.
Brown converted from the penalty spot after he was knocked over by Eric Avila in Chivas' box when he took a pass from Dillon Powers. The Rapids (2-3-2), missing six top players due to injury, won back-to-back games for the first time this season.
Chivas USA (3-2-1) missed a penalty kick near the end of the first half, struggled to create scoring chances and lost for the first time in five games.
Chivas could have tied it after Jose Erick Correa was knocked down by Shane O'Neill as he leaped for a short cross from Laurent Courtois, but Correa fired off the crossbar, and Rapids goalkeeper Clint Irwin got low to save Carlos Alvarez's rebound from 19 yards.