It's fascinating, fun, and entirely fair to wonder whether it can last.

The Phillies started the month of May on Sunday at Citizens Bank Park the same way they ended their uplifting month of April. Despite the hitters mostly being marked absent, they still managed to finish off a three-game sweep of the Cleveland Indians with a chilly, 2-1 victory that pushed them to five games over .500 at 15-10.

That's six wins in a row, nine out of 10, and zero negative thoughts in a youthful clubhouse, even though some numbers indicate trouble ahead if the offense continues to struggle.

"I choose not to look at it that way," manager Pete Mackanin said. "Those thoughts do creep in occasionally, and we know we need a little more offense. But pitching and defense wins games. That's the old adage."

It applied again Sunday for a team that has received remarkable starting pitching all season and even better work from a bullpen that was more unsettled than the Alaskan wilderness when the Phillies left spring training.

Vince Velasquez battled with a rain-soaked mound that contributed to some early control problems, but he carried the Phillies through six scoreless innings. He lowered his ERA to 1.44, the best among the team's six starters this season, but he didn't want to talk about that. He didn't want to talk about the struggling hitters, either.

"Well, we're on a winning streak, so it definitely has clicked," Velasquez said. "I think we'll be fine. We're doing great. Nothing to be worried about. Just keep on enjoying the ride and go from there."

That actually is good advice, because the players, the manager, the coaches, and fans should all be enjoying what this overachieving team is doing right now. It does not, however, change the facts about where teams like the Phillies typically end up at the finish line.

Examine baseball's 21st-century history and you'll discover just how unusual the Phillies' success was in April.

Only 26 of the 224 teams that finished April with a winning record since the 2000 season did so with a negative run differential. The Phillies, outscored by 97-80 in April, are one of 10 teams that finished with a double-digit negative run differential and a winning record.

Follow along here, because this gets better. The Phillies are one of only four teams to be at least four games over .500 at the end of April despite a negative run differential, and their minus-17 is the highest of that foursome. The Phillies' average of 3.3 runs per game in the first month was also the lowest of any team in this century to finish April with a winning record, and that number dropped to 3.28 after their latest victory.

"Obviously our offense is our Achilles' heel right now," Mackanin said before the game. "But we're able to scratch and claw and get some runs because we're always in games."

First-base coach Mickey Morandini presented a rudimentary statistic before Sunday's game that probably would have satisfied a lot of Phillies fans and the front office when the club left the Clearwater palm trees behind.

"Other than two Mets games and one Nats game, we've been in every game," Morandini said. "Being in 21 out of 24 games, that's pretty good for a team everybody predicted to lose 100 games. We'll take that."

Thanks to the pitching and the defense, the Phillies have done a lot more than stay in games. They've won them. If you saw 15-6 coming after the 0-4 start, feel free to collect your psychic diploma.

The Phillies have obviously done a lot of good things, and that extends beyond the pitching.

"We could use some more power, and those corner outfield positions are where you normally get that power from, but we just don't have it right now," Mackanin said. "But our defense in the outfield has been a bonus. That has helped us win four or five games."

Peter Bourjos' catch for the final out was an example Saturday night, and Darin Ruf and David Lough contributed a couple of terrific catches Sunday in left field.

Offense has come from some expected places - Odubel Herrera and Maikel Franco - and some unexpected ones - the catching duo of Cameron Rupp and Carlos Ruiz. Freddy Galvis, who contributed an RBI single Sunday, has been spectacular in the field and clutch at the plate.

"I think we're doing the little things late in the game," Morandini said. "We're bunting guys over. We're getting that guy in from third pretty good. We've done some things good late in the game to win."

They improved to 8-2 in one-run games and are 3-0 in extra innings.

Now back to our 21st-century history lesson.

Fifteen of the 22 teams before this season that had a winning record through April despite a negative run differential went on to post losing records. Eight of them even went on to lose 90 games. Only two reached the playoffs - the 2004 New York Yankees and 2010 Cincinnati Reds.

Those are just the facts. Forgive the Phillies if they choose to ignore them right now.

bbrookover@phillynews.com

@brookob