An own goal by Dallas' Brazilian midfielder Erick was enough for the Eastern Conference-leading Red Bulls, who claimed a 1-0 win in New Jersey.
Jonathan Steele's cross caused more problems than it should have for the Dallas defence and Erick's miscued clearance was unstoppable in the 76th minute.
Victory kept Mike Petke's New York three points clear at the top despite Sporting Kansas City's 2-1 win at Toronto.
Sapong opened the scoring on 18 minutes when he nodded in Dom Dwyer's headed pass before Darel Russell levelled seven minutes prior to the break.
Sporting goalkeeper Jimmy Nielsen's sloppy pass turned over possession and led to Russell finishing into the bottom corner from the edge of the area.
Real Salt Lake suffered a second straight loss as Steven Lenhart's brace saw the San Jose Earthquakes to a 2-1 win.
The Montreal Impact's poor form continued as they were handed a 3-0 thrashing by the Vancouver Whitecaps.
It marked Montreal's third straight loss in all competitions and sees them slip six points behind the Red Bulls.
The Columbus Crew comfortably overcame a 10-man Chicago Fire and Giles Barnes and Boniek Garcia's braces led the Houston Dynamo to a 5-1 thrashing of Chivas USA.
Juninho's 45th-minute effort was not enough for the Los Angeles Galaxy, who were held to a 1-1 draw by the Seattle Sounders.
