Playing competitively for the first time since missing the cut at last year's Senior British Open, the Monday qualifier and former PGA Tour pro was at 10-under 134 through 36 holes.
Scott Hoch, an 11-time PGA Tour winner who claimed his first Champions Tour victory this season, had a 67 to lead a group of four players who were tied for second place.
Stewart, a 53-year-old Canadian, could become the first open qualifier ever to win a Champions event wire-to-wire.
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UPI Sports Results for September 19, 2014