American tennis player John Isner’s 2012 season has been illustrative of the classic case of Dr. Jekyll and Mr. Hyde.

Isner, currently the top ranked player from the United States, has paradoxically had both the least and most successful season of his career.

At certain stages of the tennis season, Isner appeared to be immune to all pressure.

In the United States’ match against Switzerland in the first round of the Davis Cup, Isner astonished Roger Federer by beating him in four — some of the highest quality sets of tennis I have ever witnessed from him. To add to the magnitude of this breathtaking result, Isner took down Federer in Fribourg, Switzerland, Federer’s backyard.

During the Indian Wells Masters in March, Isner put togeth- er an impressive string of matches in which he conquered Serbia’s Novak Djokovic, who is currently the world’s number one player in three sets.

Isner’s upward trend continued as he took on French- men Gilles Simon and Jo-Wilfried Tsonga, which led the United States to a quarterfinal Davis Cup victory over France on clay, the surface that has proven the biggest demon to U.S. players in recent times.

In the latter part of the season, Isner won the Winston-Salem Open, defeating Tomas Berdych in the final, saving three match points in the process.

Isner reached a career-high ranking in April, becoming ninth in the world. But despite all of these accomplishments, he has failed to live up to expectation at the four majors in 2012.

Isner was defeated in the Australian Open in five sets by Spain’s Feliciano Lopez, in the French Open in five sets by Frenchman Paul-Henri Mathieu, in five sets at Wimbledon by Colombia’s Alejandro Falla and in the U.S. Open in five sets by Germany’s Philipp Kohlschreiber.

This does not mean that Isner has had a season to forget. While his Grand Slam results were not ideal, he proved that he is capable of competing with the top players in tennis.

What he needs to do now, besides build upon his physical resiliency, is integrate his heightened confi- dence into majors. But this integration must be one

that perseveres and is not shattered in the second or third round by inferior opponents. Nor can he allow himself to fall apart in the third or fourth set of an individual match.

If the young American can keep a reliable game plan intact and stick to his guns, he should prove to be of indelible value as his career progresses.