Every April sees some players to whom no one has ever paid any mind post gaudy numbers and spur much talk of improved batting stances, newly mature approaches to the game, and the like. Just as surely, every May sees most of these players begin hitting and pitching much as they always had, their early-season hot streaks as quickly forgotten as if they had happened in August.

Still, every now and again, a previously overlooked player gets off to a hot start and manages to sustain it; perhaps he has genuinely become a star, or maybe he’s just been able to play like one for a year, as Brady Anderson did in 1996. A month into the season, there’s no sure way of distinguishing the frauds from the breakouts, but some educated guesses can be made.

The best player in the National League so far has been Chicago first baseman Derrek Lee. Going into last night’s game, Lee led the league in home runs, slugging percentage, runs batted in, and OPS, and ranked second in batting average, on-base average, and runs. He has single-handedly kept the injury-riddled Cubs within range of the first place Cardinals with a .416 AVG/.495 OBA/.787 SLG batting line.

While Lee isn’t going to end the season with 200 RBI, he looks like a perfect example of a player enjoying a breakout campaign. For the last several years, Lee has been among the most consistent in the game at the plate, hitting .270 with 30 home runs, 80 walks, and double-digit steals pretty much every year while giving the sense he was capable of a bit more.

Players like Lee with a broad base of skills are more likely than one-dimensional players to improve, because they have so many ways to do so; sometimes, the improvements interact and the player takes a leap forward. In this case, Lee is being a bit more patient at the plate than usual, and hitting the ball harder when he does get his pitch. At age 29, he may simply have taken a bit longer than most to take his game to the next level. He’ll cool off, but a .320/.420/.580 season, the kind that would put him in the MVP discussion, is well within reach, and he could play at a level between that and his established one for the next few years.

When a minor star in his prime – like Lee – begins playing exceptionally well, it’s easy to deem the improvement real. When a fringe player like Brian Roberts does so, it’s easy to label it a fluke. The Orioles second baseman has hit like Lee so far this season – his .384/.465/.717 line is the best in the American League, and the biggest reason for the Orioles’ surprise start – but that’s so far out of line with what he’s done in his career that it’s easy to write off.

Lee may never have hit more than 32 home runs in a year, but he has always been the sort of hitter one could easily imagine hitting 40. Roberts, who is 27, hit eight home runs in April, which is one fewer than he had in his two previous years of full-time play. He’s not a nonentity – he set the single-season record for doubles by a switch-hitter last season and plays a solid second base. But his April was probably more about a decent player having the hot streak of his life than about a new star announcing his arrival on the national stage.

For that, you might want to look back to Chicago, where the White Sox’ Jon Garland is pitching better than anyone in the league. In April, the 25-year-old sinkerballer went 5-0 with a 1.38 ERA in 39 innings, including back-to-back complete game shutouts. Many look at his low strikeout rate of 3.92 per 9 IP and the help his defense has given him (opponents are hitting just .185 off Garland) and say he can’t sustain his success. That’s not true.

Garland’s most important stat is his groundball/flyball rate of 1.75, which is very high, indicating hitters are having real trouble driving his pitches. It’s also consistent with what I’ve seen watching him pitch – he throws a heavy ball and has finally figured out that he just needs to throw it and let the fielders do their work. He’s also stopped issuing free passes – he’s on pace to walk 39 batters in 253 innings – and has racked up three times as many strikeouts as walks. That 1.38 ERA will presumably rise, but I don’t see any particular reason to think Garland hasn’t just started fulfilling the comparisons to Kevin Brown that he has received since he was a 20-year-old rookie in 2000.

The real smoke-and-mirrors job in April was pulled off by Oakland’s Joe Blanton, a likeable, intense rookie who looks a bit like a fire hydrant on the mound and had no business whatsoever posting a 2.67 ERA in his first five starts of 2005. While Garland’s strikeout rate is very low, he has everything else going for him – a sinkerball, good control, and durability. Meanwhile, Blanton’s strikeout rate is even lower, at 2.97 per 9IP, and he’s recorded just one more strikeout than walk. And that isn’t because opponents are beating the ball into the ground – Blanton throws a variety of junk pitches, and he’s actually allowed more flyballs than grounders.

Finally, Garland has pitched around 800 more major league innings than has Blanton despite being just a year older; Blanton is limited to a fairly strict pitch count and is on pace to throw just under 200 innings. All told, he’ll end the year with an ERA closer to 5.40 than 2.70 if he keeps pitching the way he has.

Most of the other rookies and young veterans who have been on fire, like Rockies shortstop Clint Barmes, Blue Jays starter Gustavo Chacin, and Nationals starter John Patterson, are having the best stretches of baseball they’ve ever played. Quite possibly, though, one among them will be this year’s Carlos Guillen, someone making a vast, sudden, and unexpected leap into the game’s elite class. Which among them? Who knows? We’ll find out soon enough.