An easily-overlooked highlight of the depressing end to the Pirates' 2012 season was the final starts of a pair of 25-year-old pitching prospects.

On Sept. 29, right-hander Kyle McPherson blanked National League Central champion Cincinnati for six innings.

Two days later, lefty Jeff Locke allowed one run in six innings against another playoff-bound team, Atlanta.

Those strong last impressions seemed to cement the roles of McPherson and Locke as at least frontrunners to crack the Bucs' 2013 rotation. As recently as a week ago, that plan was in place.

Then, everything changed. First the Pirates re-signed Jeff Karstens, and shortly afterward came to a re-worked agreement with free agent left-hander Francisco Liriano.

Suddenly, all five seats in Pittsburgh's rotation again are occupied by veterans, with the incumbents being A.J. Burnett, Wandy Rodriguez and James McDonald. Displaced are a couple guys who a few months ago had been deemed integral enough to be prioritized over a full-boar shot at ending a record streak of losing seasons.

If you'll recall, the Pirates went down the stretch with Locke and McPherson, and went 2-7 in their starts while overall finishing at 79-83. One of the pitchers ironically displaced by their showcase was Karstens, who, though healthy by then, worked a total of 7 1/3 relief innings in September.

Less than three weeks before the Pirates' first Spring Training workout for batterymates in Bradenton, Fla., Locke and McPherson may be back in the wings, as opposed to center-stage, but they remain as critical as ever.

Boosted by their experiences of last September, even if they start the season back in Triple-A, in the event of injuries they will provide more solid and dependable help than the Bucs could count on in recent years. Liriano's status won't be fully known until he's in Pirate City, but if his broken right arm delays his season, someone will have to fill in for him in the early going.

Because of the importance of rotation depth, neither figures to factor into an overhauled bullpen. Joel Hanrahan, Chris Resop and Juan Cruz -- who had 167 appearances among them last season -- are gone. However, if a move to the bullpen for either young starter gets some consideration, Locke will be more likely to transition.

McPherson is the hard thrower who could bring more gas from the bullpen. But Locke is a left-hander -- manager Clint Hurdle would like a second southpaw next to Tony Watson -- whose stuff may play better in short spurts.

Not only has Locke been consistently victimized by big innings, but they usually occur during his second and third times through a lineup. Batters getting their first looks at him in 2012 went 12-for-51 (.235) with one homer and fanned 16 times; thereafter, they jacked those numbers to .328 (23-for-70) and five homers.

When Locke did work in relief last season, he was lights-out. Locke allowed one hit in 4 1/3 shutout innings, without a walk -- managers love to wave to the bullpen for guys who will enter throwing strikes.

Though they lead the pack, Locke and McPherson aren't the only ones affected by the recent moves.

There is Kris Johnson, the Minor League veteran lefty who just finished a dramatic offseason of rebirth in the Dominican Winter League as the ace of champion Escogido. Johnson went Derek Lowe -- recall him in 2004 winning clinchers for the Red Sox in the American League Division and Championship Series, and the World Series? -- in pitching the games that got Escogido into the playoffs and into the finals, where he finished off a five-game sweep of Aguilas. Regular and postseason combined, Johnson allowed 37 hits -- no home runs -- and six earned runs in 59 1/3 innings (0.90 ERA) with a 50-to-13 strikeouts-to-walks ratio. That will get the attention of a lot of people.

Andy Oliver (acquired from Detroit in a trade) is another lefty, a former second-round Draft pick with limited big league experience. Jeanmar Gomez (acquired in a trade from the Indians) has even more Major League experience and the Bucs are the latest to hope the Vin Mazzaro (acquired in a trade from Royals) lightning that flashed in 2009 -- he began his career with a 17 2/3-innings scoreless streak, an A's record -- can strike again.

In the periphery, organizational jewel Gerrit Cole casts a shadow that could grow with an undeniable spring. And don't forget about Charlie Morton, who is on track while recovering from midsummer Tommy John surgery and could become a factor by late July.

That's a lot of depth, adhering to the time-tested belief that "you can't have too much pitching." Whether the Pirates have good enough pitching -- only more time will tell.