Lowly Atlanta was upstaged by FC Dallas 2-1 on Saturday – leaving De Boer's side without a victory at home in the league this season.
Atlanta attempted 22 shots at Mercedes-Benz Stadium, where Jesus Ferreira and Bryan Acosta silenced the hosts.
Josef Martinez converted a penalty deep into stoppage time but it was merely a consolation for Atlanta, which has only won three games in all competitions since former Inter and Crystal Palace boss De Boer replaced Gerardo Martino.
Plenty of chances to build on.— Atlanta United FC (@ATLUTD) April 21, 2019
Highlights from today's match pic.twitter.com/yWSk2Rsea5
Atlanta is second from bottom in the Eastern Conference with five points from six matches, while Dallas are fourth in the Western Conference.
Elsewhere, ex-Manchester United winger and Portuguese star Nani led Orlando to a 1-0 win against the visiting Whitecaps.
Nani deflected Sacha Kljestan's 88th-minute shot beyond Vancouver goalkeeper Zac MacMath for his fourth MLS goal since arriving from Sporting CP.
After Colorado's Kei Kamara canceled out Nemanja Nikolic's opener prior to halftime, the Fire scored three unanswered goals following the break via C.J. Sapong, Djordje Mihailovic and Aleksandar Katai.
Rapids midfielder Jack Price was sent off with four minutes remaining in Chicago to compound Colorado's misery.
Elsewhere, New England edged New York Red Bulls 1-0, Portland Timbers ended their winless start to the season by defeating Columbus Crew 3-1, Philadelphia Union accounted for Montreal Impact 3-0 and the San Jose Earthquakes crushed Sporting Kansas City 4-1.