WHAT IT MEANS: The Mets opened the second half by getting swept in a three-game series in Atlanta, capped by a 6-1 defeat Sunday afternoon.

Pitching coach Dan Warthen was ejected by plate umpire C.B. Bucknor over the strike zone after Michael Bourn’s RBI double gave Atlanta a 1-0 lead during what became a six-run fifth inning by the Braves against Johan Santana. Santana also jawed with Bucknor, as the southpaw left the field following an inning that included a three-run homer by Freddie Freeman.

Since Santana’s June 1 no-hitter, he is 3-4 with a 5.67 ERA in seven starts.

Santana had surrendered seven runs and 13 hits in 4 2/3 innings against the Cubs in his final first-half start, in an outing in which he twisted his right ankle. He has now allowed six-plus runs in consecutive starts for the first time since April 2000 -- in the third and fourth appearances of his major league career.

Ramon Ramirez replaced Santana for the sixth inning. Santana’s final line: 5 IP, 8 H, 6 R, 6 ER, 2 BB, 3 K.

Ben Sheets, in his first major league action since July 19, 2010, limited the Mets to two hits and a walk in six scoreless innings.

The Mets went swept for the fourth time this season (also by Houston, the Yankees and Cincinnati). They dropped to 46-43 -- 6½ games behind the first-place Nationals, who won at Miami. Atlanta occupies second place in the division, at 49-39.

WHAT’S NEXT: The Mets spend an off-day in D.C. before opening a three-game series at Washington. Jon Niese (7-4, 3.73 ERA) will oppose left-hander Ross Detwiler (4-3, 3.43) in Tuesday’s series opener. Jason Bay could return from the disabled list for that game. He went 2-for-4, walked and stole a base while playing left field for nine innings with Triple-A Buffalo on Sunday at Pawtucket.