Cubs pitcher Arrieta struck out eight with one walk and allowed five hits in his first seven-inning outing since June 11.
Syndergaard was just one out shy of officially getting a quality start, also striking out eight with two walks and seven hits while throwing 105 pitches in 5.2 innings.
Rene Rivera delivered the key moment in the ninth for the Cubs, with his two-out RBI single decisive.
The Boston Red Sox shut out the San Francisco Giants 4-0, the Detroit Tigers went down to the Minnesota Twins 6-2 and the Atlanta Braves needed 11 innings to get past the Cincinnati Reds 5-4.
Aaron Sanchez starred as the Toronto Blue Jays claimed a 5-1 win over the Arizona Diamondbacks and the Cleveland Indians were 7-3 victors against the Kansas City Royals.
The New York Yankees were untroubled in a 7-1 win over the Baltimore Orioles, the Tampa Bay Rays thrashed the Colorado Rockies 10-1 and the Oakland Athletics overcame the Houston Astros 4-3.
The Pittsburgh Pirates had a 3-2 walk-off win over the Milwaukee Brewers, the Miami Marlins were 2-1 winners over the Philadelphia Phillies and the Los Angeles Dodgers beat the Washington Nationals 8-4.
The Chicago White Sox beat the Seattle Mariners 6-1 and the Los Angeles Angels edged the Texas Rangers 8-6.
The meeting between the San Diego Padres and St Louis Cardinals was washed out. UTLEY LEADS OFF IN STYLE
Los Angeles Dodgers second baseman Chase Utley made the most of the leadoff spot with three hits, including a first-inning homer, and three RBIs against the Nationals. ORTIZ GOES DEEP
David Ortiz's 442-foot home run in the fourth inning against the Giants scored three at Fenway Park.
— MLB (@MLB) July 20, 2016
BAD DAY FOR LOS ANGELES
Tuesday was not a good day for Los Angeles pitchers. After Dodgers ace Clayton Kershaw was indefinitely shelved, Angels right-hander Nick Tropeano had an MRI on his right elbow that revealed a high grade tear of his ulnar collateral ligament. Tropeano will seek a second opinion to determine the appropriate course of action, but Tommy John surgery is likely. Tropeano is 3-2 with a 3.56 ERA and 68 strikeouts in 68.1 innings in 13 starts. INDIANS, ROYALS DO BATTLE
There might not be many runs scored in this one with both starting pitchers throwing really well as of late. Cleveland's Carlos Carrasco (6-3, 2.49 ERA) has a 1.76 ERA with 47 strikeouts and 14 walks in 46 innings over his last seven starts. Kansas City's Ian Kennedy (6-7, 3.86) has not allowed more than three runs in a start since June 15.