Yuki struggled to find his touch in a 4-6 6-2 6-4 win over Serbia's Nikola Milojevic, whereas a profligate Ramkumar Ramanathan lost 6-7(6) 6-7(5) after being in command against third seed Spaniard Adrian Menendez-Maceiras.
Yuki never played like a top seed and someone who was in authority, and it was the 319th ranked Serb, who dictated terms before losing the plot.
By his own admission Yuki made it tough for himself by not being able to execute the plan. He had saved his best perhaps for the last when he broke Milojevic to seal the match.
"But it is important to get through. He hit the ball flat. I was defensive and had no control. I also lost concentration. He came out playing freely and it happens when you play as underdog," he added.
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Milojevic's forehand was better than his backhand but he used his double-handed backhand to good effect, surprising Yuki on a few occasions.
23-year-old Yuki, ranked 105, took some time to settle down and stave off a break chance in the opening game before managing to hold. He started off with a double fault and following errors put him down 30-40 before he served well to push the danger away.
Yuki fought back and induced errors from the Serb after fierce rallies to earn three break chances. The second was converted when Milojevic sent a forehand soaring over the baseline and the match was back on level terms 3-3.
A flurry of errors again put Yuki down by three break chances. He saved two but hit a forehand on the third and the Serb was now serving for the set.