Rosenkranz was a world-class bridge player and one of the most successful in Mexico.  He won 12 NABC-level events at thrice-annual North American Bridge Championships meets, including all four major  titles: the Grand Nationals, Reisinger, Spingold and Vanderbilt. In world championship teams competition, he represented Mexico in the quadrennial World Team Olympiad three times from 1972 to 1996 and the United States in the 1983 Bermuda Bowl. In addition, he has made significant contributions to bidding theory. He created the Romex bidding system, an extension of Standard American with many gadgets. He invented the Rosenkranz double and Rosenkranz redouble, and wrote more than a dozen books on bridge.