[3][9] In 1984, at age 11, he was the overall winner at the International Optimist Dinghy National Sailing Championships in Maryland, and also won the North American title.

[17] In college, he was a three-time All-American in sailing (1992–94), and was named winner of the Clarence "Pop" Houston Award as Tufts University Athlete of the Year in both 1993 and 1994.

[8][18] Mendelblatt earned a silver medal in the Laser at the 1999 Pan American Games on Lake Winnipeg, behind Brazil's Robert Scheidt and ahead of Diego Romero of Argentina.

[9] He won the 2003 Rolex Miami Olympic Class Regatta, the Laser Pacific Coast Championships in Oregon on the Columbia River (coming in first out of 33 boats),[2] and the Laser Gulf Coast Championships in Texas (coming in first out of 56 boats), and was named US Sailing's 2003 United States Olympic Committee Male Athlete of the Year.

[9] Tim Landt, president of the International Laser Class Association, said Mendelblatt was "the total package", opining that: "He's got the perfect structure (6 feet 2, 180 pounds).

[25] That month, he also won the two-person racing keelboat Star class 78th Bacardi Cup on Biscayne Bay, with Mark Strube as crew.

[27] In August 2006, he and Strube won the Star European Championship over 93 boats in Neustadt, Germany, again defeating second-place finishers Scheidt and Prada.

[28][29][30] Mendelblatt accepted a position in the fall of 2006 with Emirates Team New Zealand, and in April 2007 replaced injured veteran Adam Beashel.

[33] In June 2011, he and Brian Fatih won the Star class medal race at the Skandia Sail for Gold Regatta in Dorset, England.