But the Giants found their fit with Leake, who's 9-5 with a 3.56 ERA in 21 starts.
"I feel like we've got more depth that will give us a good chance to win, day in and day out," Evans said.
Skeptics might claim that Leake, 27, isn't a significant upgrade over most Giants starters, such as Matt Cain, Tim Hudson and Jake Peavy. San Francisco's starters are 10-2 with a 3.35 ERA in the team's past 15 games but have averaged approximately six innings per outing.
By contrast, Leake worked eight innings in three of his past four starts, winning all of them and recording an 0.60 ERA in that span.
"We've been in touch with Cincinnati about Leake since Day One," Evans said.
In six seasons with the Reds, Leake compiled a 62-47 record with a 3.87 ERA. Relying primarily on command, Leake has averaged only 2.3 walks per nine innings while accumulating 701 strikeouts in 1,028 1/3 career innings.
"He's not going to overpower guys, but he's going to be consistent," Evans said.
Leake also could benefit from switching home fields. He owns a 4.31 lifetime ERA and a .276 opponents' batting average at hitter-friendly Great American Ball Park in Cincinnati, compared with 3.43 and .256 on the road.
Leake's impending arrival forces short- and long-term issues upon the Giants. The venerable Hudson likely will be removed from the starting rotation; Evans said he addressed this matter in telephone conversations with the 40-year-old right-hander and his agent. Asked to describe Hudson's reaction, Evans said, "He ultimately wants to see the club excel and win."
Also, Leake is eligible for free agency after this season, so there's no telling how long he'll remain a Giant. His 2015 salary is $9.78 million. Because Leake was traded during the season the Giants cannot give him a qualifying offer and therefore will be unable to recoup Draft pick compensation should he sign elsewhere.
San Francisco didn't acquire Leake easily. The 21-year-old Mella, who finished 5-3 with a 3.31 ERA in 16 starts for Class A Advanced San Jose, was ranked by MLB.com's MLB Pipeline as the top prospect in the Giants' organization. Duvall, who displayed slugging prowess but never could settle in at a position, led the Pacific Coast League with 26 home runs for Triple-A Sacramento. He also batted .279 with 25 doubles and 79 RBIs in 99 games.