The Reds have won 13 of 14 to establish baseball's best record as they host the team chasing them in the NL Central - the wild card-leading Pirates - on Friday night.
Cincinnati (64-41) and Pittsburgh (60-44) could both be headed to the postseason for the first time since the Reds eliminated the Pirates in six games in the 1990 NLCS en route to their last World Series title.
Pittsburgh has won 11 of 16 since July 16, but Cincinnati has taken 14 of 17 in that same span - all without injured star Joey Votto - to build a 3 1/2-game lead in the division.
The Reds took three of four at home from San Diego capped by Thursday's 9-4 victory. Todd Frazier homered in a six-run second inning and finished with three RBIs.
"You want to have big innings every game," said Frazier, who has homered in three of his last five contests. "We had the big six-run second, and everybody contributed. We batted around.''
Second baseman Brandon Phillips has missed the last two games with a strained left calf, and it's unclear if he will return for this series.
The Pirates are 5-4 against the Reds this year. These teams haven't met since early June, and Pittsburgh is eager for the chance to gain ground.
"We know when we go in there this week, it's time to win," reliever Jared Hughes told the Pirates' official website. "There's no other option. We're going in there, and we're winning."
The Reds have fared well against Andrew McCutchen, whose .231 average in the season series is his second-worst against an NL club. McCutchen raised his major league-best average to .373 by going 6 for 11 with three walks this week as the Pirates took two of three on the road from the Cubs.
The Pittsburgh star is 0 for 1 with two walks against Mat Latos (9-3, 4.17 ERA), who is 3-0 with a 2.16 ERA in four career starts against the Pirates. Latos struck out 11 over six innings May 6 in a 5-0 victory in his lone start versus Pittsburgh this year.
The right-hander won his second straight outing Sunday by allowing two runs over eight innings in a 7-2 victory at Colorado.
Latos will be opposed by Wandy Rodriguez (7-9, 3.82), who will make his second start for the Pirates since being acquired last week from Houston. Rodriguez faced his former team in his first outing, giving up three runs with a season-high five walks over six innings Saturday as he did not get a decision in a 4-3 victory.
"I thought he was probably excited to get out there and pitch," manager Clint Hurdle said. "I have never seen him walk five in a game all of the years I have watched him pitch. I'm sure he had some emotion or adrenaline.''
The left-hander is 1-1 with a 6.35 ERA in three starts against the Reds this year with the Astros. He won't miss facing Votto, who hits .378 against him, while Jay Bruce is 2 for 29 with 15 strikeouts.