Complex sentence: He is currently the Swiss No.1 and World No.3, which is also his career-high singles ranking, attained on 27 January 2014 as a result of winning his first Grand Slam event, the 2014 Australian Open.
Split into simpler sentences: He is currently the Swiss No.1 and World No.3, which is also his career-high singles ranking. He first attained this ranking on 27 January 2014 as a result of winning his first Grand Slam event, the 2014 Australian Open.