Nishikori, who lost to Rafael Nadal in the Monte Carlo Masters final on Sunday, pulled out after conceding the first set to Garcia-Lopez 6-3.
A win there will see him face one of Klizan or Feliciano Lopez in the quarter-finals.
"But obviously there's a guy named Rafael Nadal who is always on the way to winning more "big titles" and he still keeps on dominating this surface, and he's definitely always the guy to beat". He won the match 6-4, 6-4 in a match that almost lasted two hours.
The 16-time Grand Slam champion, who is now working with former world No. 1 Carlos Moya, has said he would love to have Toni back, although he joked that he never asked his uncle to leave.
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It's been forever since they had a future franchise quarterback and now they are in a position to address it once and for all. Petty was a fourth-rounder in 2015, while Hackenberg went in the second round in 2016. "He is a good football player".
"I felt pain in three different parts of my body while warming up, and wasn't able to perform to my best", he said.
"He [Garcia-Lopez] is aggressive, he has good punches and good service, he will not go out on the court without believing he can win, he has experience in important matches".
Nadal has only ever lost three times in Barcelona, and has now won 38 consecutive sets on clay and once he'd warmed to his task here, he proved too strong for his impressive Spanish compatriot.
Having received a first-round bye, Nishikori pulled out in the first game of the second set of his second-round match against Spain's Guillermo Garcia-Lopez, after losing the first set 6-3.
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She said the court "has impartially and without prejudice presided over numerous proceedings in this matter since 2008". Needlesstosay, the internet joined in the frenzy to celebrate Meek's release.
He set up the foundation for victory by winning nine straight games from 1-1 in the first set to 4-0 in the second set against Garcia-Lopez, the 34-year-old world number 69.
Elsewhere, second seed Grigor Dimitrov of Bulgaria saved two match points to beat Tunisia's Malek Jaziri 7-5 3-6 7-6 (10-8).
Thiem, who was hammered by Nadal in the Monte Carlo quarter-finals last week, had little trouble in beating Slovakian lucky loser Jozef Kovalik 7-6 6-2 and he will face Stefanos Tsitsipas for a place in the last four after the Greek teenager ousted 10th's seed Albert Ramos-Vonolas.
He hasn't made it past the last 16 in five tournaments this year.
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Martin says that a book on the history of fictional world Westeros called Fire & Blood will be available to purchase this year. In addition to the 989 manuscript pages of content, the book will also feature illustrations by Doug Wheatly.