Pedro Guerrero homered and drove in both of his team's runs yesterday in Cincinnati, enabling Fernando Valenzuela to become the National League's first nine-game winner as the Los Angeles Dodgers beat the Reds, 2-1.

Guerrero drove in a run in the first inning when he reached first base on an error, then broke a 1-1 tie with a home run in the seventh inning to give the Dodgers their fifth straight victory.

Valenzuela (9-5) gave up five hits in beating the Reds for the first time in his career and pitching his eighth complete game of 1982. The left-hander retired the last 12 batters in outdueling Bruce Berenyi (5-7).

''I am just doing my thing,'' said Valenzuela, who reported late to training camp because of a contract dispute after winning leage Cy Young and rookie of the year awards. ''I am just doing what I know.

"So far this year, I've felt very happy with the way I've pitched," Valenzuela said through an interpreter. "When I've won, I've felt great, really." Most of the games have been very close. When I have won, I've been very pleased with myself."

Cesar Cedeno homered in the second inning for Cincinnati's run. It was his sixth of the year, third of the week.

The Dodgers' first run was set up by singles by Steve Sax and Ken Landreaux. A double steal put both runners in scoring position and shortstop Dave Concepcion made an errant throw to first base on Gurerero's grounder as Sax scored.

Valenzuela was touched for a hit in each of the first five innings before breezing in.

"He never ceases to amaze me," said Dodger Manager Tom Lasorda. "He's a tremendous closer (complete-game pitcher). There's not too many of them around.

"He's what I call a super closer," Lasorda said. "You get him in the seventh, eighth and ninth inning with a one-run lead, and he becomes very tough."

The victory boosted the Dodgers to two games over .500, and dropped the Reds to 27-37, still in last place in the National League West.

"I'm very happy to be No. 1 in the win column," Valenzuela said. "I am happier with the fact that the team is winning."