Gio Gonzalez had not given the Washington Nationals reason to worry before Tuesday night, but he had been veering toward that direction. They never doubted their left-handed, ever-smiling all-star, but Gonzalez had fallen off the pace that made him an early-season Cy Young candidate. His relative slide culminated last week, when he allowed the New York Mets six runs in less than four innings. Five days later, against the same New York Mets, Gonzalez delivered a gem, one of the best starts of a season whose game log reads like a greatest hits collection. In a 5-2 victory at Citi Field, Gonzalez allowed no earned runs in seven efficient, dominant innings. He yielded two hits, walked two and threw only 87 pitches. The performance put to rest any worries and smothered any doubts.