Kei Nishikori exited from the quarterfinals of the ABN AMRO World Tennis Tournament in Rotterdam on Friday, losing a tight two-setter to Croatia's Borna Coric 7-6(2), 7-6(4).World No. 45 Nishikori, who missed most of the 2020 season following major elbow surgery, blamed a lack of concentration for his loss of two tiebreakers against the 26th-ranked Coric."I'm disappointed because I had the chance to win (but) I made a lot of mistakes," Nishikori said. "I tensed up because I started thinking too much about wanting to win."The former world No. 4 aims to work his way back to the top 10 followi…READ FULL ARTICLE