AUGUSTA, Ga.—The pressure was even more than Hideki Matsuyama could have imagined when he stood on the first tee Sunday at Augusta National. So was the emotion when he walked off the 18th green as the first Masters champion from golf-mad Japan. His arms securely inside the sleeves of the green jacket, he thrust them in the air. Ten years after he made a sterling debut as the best amateur at the Masters, the 29-year-old Matsuyama claimed the ultimate prize and took his place in history. Whether he’s Japan’s greatest player is not his concern. “However, I’m the first to win a major,” he said through his interpreter. “And if that’s the bar, then I’ve set it.” Staked to a four-shot lead, the nerves stayed with Matsuyama from the time he hit his opening tee shot into the trees to back-to-back birdies that led to a six-shot lead to a …