Note: This story was originally posted on Sunday, July 20, and was updated and revised on Thursday, July 24.

MADRID, SPAIN — Alex Zhai tied for first place at the 49th International Mathematical Olympiad as he won his second gold medal in two years and led the six-member U.S. team to a third-place finish overall.

Zhai scored the maximum possible 42 points in the six-problem, nine-hour contest, which took place Wednesday, July 16, and Thursday, July 17. Results were announced this weekend.

Two other competitors, Xiaosheng Mu and Dongyi Wei, both from the People's Republic of China, also scored 42 points and tied the 2008 Uni alum for first place.

The U.S. team won four gold medals and two silver, finishing with 190 points. The Americans placed third, their best performance since 2005, when the U.S. was second.

China won this year's contest with 217 points. Russia was second with 199. A total of 535 students from 101 countries competed.

The five other U.S. team members finished as follows:

• Colin Sandon, Essex High School, Essex Junction, Vt.
  gold medal, 35 points, 12th place
• Shaunak Kishore, Unionville High School, Kennett Square, Pa.
  gold medal, 32 points, 35th place (tie)
• Krishanu Sankar, Horace Mann School, Riverdale, N.Y.
  gold medal, 32 points, 35th place (tie)
• Evan O’Dorney, Berkeley Math Circle, Berkeley, Calif.
  silver medal, 26 points, 78th place
• Paul Christiano, The Harker School, San Jose, Calif.
  silver medal, 23 points, 116th place

Zhai is the first U.S. competitor to earn a perfect score since Brian Lawrence of Montgomery Blair H.S., Silver Spring, Md., achieved the feat in 2005.

The best American performance occurred in 1994, when all six team members earned perfect scores and the U.S. placed first. America began competing in the IMO in 1974 and has won four times: in 1977, 1981, 1986, and 1994.

The IMO is often referred to as the world's toughest math contest, putting a premium on mathematical creativity in solving problems that cover geometry, number theory, algebra, and combinatorics. To see this year's problems, click here.

This was Zhai's third consecutive appearance in the IMO. After his sophomore year at Uni, Zhai won a silver medal and tied for 49th place individually at the 47th IMO, held in Ljubljana, Slovenia, in July 2006.

A year later, Zhai won a gold medal and tied for seventh at the 48th IMO, held in Hanoi, Vietnam.

In both of those competitions, the U.S. team placed fifth. Zhai and his teammates from the 2006 IMO were the subject of a recently released documentary film, "Hard Problems."

This year Zhai also made the 24-student U.S. Physics Team, although he did not compete in the International Physics Olympiad in Hanoi, which was limited to five students per country.

Zhai plans to attend Harvard University this fall.