George Frazier walked Andres Thomas on four pitches with the bases loaded and one out in the 13th inning to give the Braves a 9-8 victory over the Chicago Cubs, 9-8, last night in Atlanta.

The Braves, who had 21 hits, have won sixth straight. The winning run was unearned because Bob Horner reached on third baseman Manny Trillo's error to open the 13th. Pitcher Jeff Dedmon forced Horner and took third on Rafael Ramirez's fourth double of the game, which tied a major league record. Ozzie Virgil was walked intentionally to bring up Thomas.

The Cubs gained an 8-8 tie with two outs in the ninth when Jody Davis hit a three-run homer off relief ace Bruce Sutter.

*Pirates 2, Astros 1: Rick Rhoden pitched a five-hitter and Sid Bream got a double and his seventh home run to lead Pittsburgh in Houston. Rhoden (3-3) walked three and struck out six in his first complete game of the season.

Bream opened the Pirates' second with a double to center off Mike Scott (4-3). Mike Brown singled to right, sending Bream to third, and Jim Morrison singled to give the Pirates a 1-0 lead.

*Mets 7, Giants 4: Wally Backman had two doubles and a single and Ron Darling allowed three hits over seven innings as New York won in San Francisco.

Darling (5-0), who had a four-run lead before he threw his first pitch, struck out four and walked four. He left with a 7-2 lead. Roger McDowell gave up RBI doubles to Chili Davis and Bob Melvin.

The hits off Darling included Chris Brown's RBI triple in the first inning and Dan Gladden's homer in the third. Roger Mason (2-4) lasted only 2 2/3 innings and was charged with all the Mets' runs.

The Mets, who have averaged 6.5 runs behind Darling, have won all eight of the games he has started this season. He has won 11 of his 12 decisions since Aug. 19.

*Cardinals 8, Reds 3: In St. Louis, Andy Van Slyke's first home run of the season highlighted a four-run sixth inning that helped the Cardinals end a six-game losing streak.

The Reds were trying to win three in a row for the first time this season. They left 11 runners, 10 of them in the first five innings.

*Padres 7, Phillies 2: In San Diego, Dave Dravecky pitched a four-hitter and struck out a career-high 11. Teammate Tony Gwynn went four for four to take the NL batting lead at .362.

Dravecky (4-3) allowed three hits in the third inning when Philadelphia scored its runs. It was his second complete game of the year.

*Dodgers 6, Expos 1: Mike Marshall homered twice, drove in three runs and scored three times to enable Orel Hershiser to win in Los Angeles.

Hershiser (4-3) allowed four hits in seven innings and helped himself with a hit and an RBI. Ken Howell finished.

Marshall raised his home run total to 10 and RBI to 32, tying him with Hubie Brooks of the Expos for the league lead in both categories.