Daniel Mengden and Chris Bassitt are the odd men out, but they'll be readily available at Triple-A Nashville while Andrew Triggs (arm nerve irritation), Paul Blackburn (elbow) and Daniel Gossett (elbow) remain sidelined for now.
"It's nice that we're getting guys back right now," Melvin said. "We'll see where this five goes right now. Knock on wood, we don't have as many injuries as we did the first half, but when Mengden is pitching well, he pitches as well as anyone on our staff. My guess is we'll see him at some point, but I'm not really sure when."
Montas, who is penciled in for a Tuesday start in Arlington, has been one of their better performers, pitching to a 3.35 ERA in eight outings following his May 27 promotion. A Tuesday start with Nashville allowed the right-hander to get regular work during the break; he tossed five scoreless innings with just three hits allowed.
Eleven different starters have made at least five starts for the A's -- two more than any other team -- and the club has employed 12 overall. Yet they entered Friday's contest with the Giants 13 games over .500, much thanks to a rolling offense and a sturdy bullpen.
A's starters have been doing their part of late, too, compiling a 3.36 ERA over the last 17 games.
"We felt all along we could get better as the season went along," Melvin said. "That's been the case. We're playing our best baseball at this point, so it's more about going out there every day with the expectation to win and try to gain some confidence from the stretch that we've been in.
"We don't worry about who we're playing next, road, home, or whatever, it's more about focusing on winning a particular game."
• Outfielder Matt Joyce (lumbar strain) is expected to resume baseball activities within a few days after recovering from an epidural shot.
• The A's will open Mount Davis for the first time in 13 years for Saturday's game against their Bay rivals. Tickets are $10 and fans will have access to limited food and beverage options, including $2 hot dogs, nachos, peanuts, bottled water and soda.
By opening these sections, the A's will bring the total Coliseum capacity to 56,782. The attendance record of 55,989 was set June 26, 2004 against the Giants.
"The more people you can get in this ballpark," Melvin said, "the better it is."
Jane Lee has covered the A's for MLB.com since 2010.