A stalwart of Boothbay Harbor tennis for seven decades, Dan Hazelton, just distinguished himself at the World Tennis Championships in Mallorca, Spain where 800 players from more than 40 countries competed in a range of age groups.    Playing for the first time in the 80 and over division, Hazelton of Juniper Point starred in three separate competitions. He reached the finals of the mixed doubles with a Swiss partner, the semis of the men’s doubles with a Canadian partner and the round of 16 in singles. Playing against the world’s best players, Hazelton defeated the number ones from Argentina and Brazil before running into the world’s number three.    Hazelton is part of a great Boothbay region tennis tradition. Squirrel Island long hosted a major national level tournament in the late summer and the clay courts of Ocean Point, Juniper Point, the BH Yacht Club, and other communities have produced a generous share of college level competitors. Hazelton prepared for the tournament with local players including coach Susan Kirby at the beautiful new indoor YMCA courts.