For the first 14 months of his professional career, Sam Querrey made tennis look pretty easy. From January 2006 to February 2007, the 6-foot-6-inch Californian, who passed up a full scholarship to the University of Southern California to turn pro, climbed the rankings like shares of Google: In a little more than a year he rose to 66 from 616 with nary a dip. At the Australian Open, Querrey was all smiles as he won two rounds at a major for the first time. His strategy, he said, was simple — smash serves, slug forehands, and let the balls fall where they may.

Alas, top tennis prospects, like stocks, are bound to level off, or drop precipitously, before reaching a peak. At various times in the last six months, Querrey has played impatiently, or seemed to lack confidence. From the end of April until two weeks ago, he lost seven consecutive matches, including a first-round loss at the French Open (not too surprising) and Wimbledon (surprising, considering his opponent was Alejandro Falla). Before he arrived in Indianapolis last week, Querrey’s ranking had fallen to 91.

Just a slump, or a sign that expectations for Querrey might have been too high? It’s a difficult question to answer when we’re talking about a player who won’t celebrate his 20th birthday until October. Still, Querrey’s performance in Indianapolis this week, and his stats for the season so far, suggest he should have a lot more ups than downs in the years to come.

On Saturday, Querrey secured his first victory over a top 10 player, defeating James Blake, the formerly fabulous American whose decline continues apace, 7–6(6), 6–7(4), 7–6(4) for a spot in the semifinals. Rain stalled the tournament earlier in the week, so Querrey had to play again that afternoon, and things didn’t go as well against Dmitry Tursunov, the eventualchampion. AgainstBlake, though, he showed how dangerous he can be.

Querrey served 34 aces in the match and didn’t face a single break point. In one stretch, he hit 10 consecutive aces: one to end the first set, followed by two love games and an ace to begin his next service game. The ATP couldn’t decide whether that was an Open Era record — it was “believed to be,” the tour said — but record or not, it was ridiculous. One never sees that many aces in a row at any level, never mind against a player the caliber of Blake.

Since Querrey became a pro, his serve has brought him most of his success. This year he’s fourth on the tour in aces (402), and fourth in aces per match (12.7). He wins 81% of his service games, tied for 10th on the tour, and he is among the leaders in break points saved, too.

As impressive as those numbers are, they ought to be better. Querrey’s serve has a lot of room for improvement. One flaw in particular stands out: He misses his first serve too frequently. For someone who hits so many aces, and wins service games so consistently, Querrey has a below average first-serve percentage (56%). Compare that to Ivo Karlovic’s 67%, Andy Roddick’s 66%, Roger Federer’s 60%, and Ivan Ljubicic’s 59%. Querrey’s height, which allows him to strike the ball at a more favorable angle, and solid mechanics (a simple motion and a low toss) ought to give him an advantage in this regard. There’s no reason why he shouldn’t consistently serve a percentage that’s closer to the mid-60s than the mid-50s, as he did against Blake on Saturday (64%). If he does, his serve alone ought to carry him inside the top 20. If his forehand and footwork improve, the top 10 won’t be out of reach.

All sports fans are guilty, at one time or another, of adopting extreme opinions despite scant evidence. At last year’s U.S. Open, I watched Donald Young, the much-hyped world no. 1 junior, with a fellow sportswriter who shall remain nameless. My colleague came to the match skeptical of Young, who had endured several beatings in previous months. By the time Young had won the first set of his first-round match against Novak Djokovic, my colleague was a believer. But his conviction wavered when Young lost the second set, and as Djokovic polished off the third set at love, conviction had transformed into hysterical doubt and concern for the mental health of a child. Young had gone from surprisingly improved to immature, and even helpless, in the s pan of an hour.

The point here is not to disparage a colleague, but to illustrate that in tennis, the temptation to make quick, ill-advised judgments is particularly strong, as a player succeeds and fails on his own, with no teammates to either hide his flaws or give us reason to excuse his successes as flukes. Marion Bartoli, the surprise Wimbledon finalist, looked all but invincible a few weeks ago, no matter how overweight she was. Last week, she lost in the second round in Stanford, Calif., to Lilia Osterloh, who is ranked 106 in the world. Frank Dancevic, a 22-year-old Canadian who had not won consecutive matches in a pro event in four years on the tour, reached yesterday’s final in Indianapolis, beating an ill Roddick along the way. Sania Mirza had struggled for months before she made the Stanford final yesterday, where she lost to top seed Anna Chakvetadze.

Will the careers of these three players change radically because of their performances this last week? Probably not. Will Querrey now consistently reach semifinals, less than a month after he couldn’t win a match? Again, no — don’t be surprised if he plays poorly the rest of the season, if only because he’s young. Yet there shouldn’t be any doubt that he’s capable of excellent results in the future. Men of his size with two weapons and a positive attitude are not common. In time, Querrey ought to show that his victory over Blake was just the beginning.

tperrotta@nysun.com