2014 has been Marin ##ković 's most successful year . but I learned a lot of things , '' explained the world no . 9 . ` 26-year - old won four titles , including first major grand slam , the U.S. Open , in September . Croatian has had to wrestle back credibility after failed drug test in April 2015 . Big ##ić says his time out of the game has contributed to his fantastic results .
2014 has been Marin ##ković 's most successful year . 26-year - old won four titles , including first major grand slam , the U.S. Open , in September . Croatian has had to wrestle back credibility after failed drug test in April 2015 . Big ##ić says his time out of the game has contributed to his fantastic results .