Forty drivers started Saturday’s U.S. Cellular 250 at Iowa Speedway, but it was just a two-horse race with rookie Erik Jones and Ty Dillon combining to lead all but thirteen of the laps run.  When the dust settled, it was Jones parked in Victory Lane with his Number-20 Joe Gibbs Racing Toyota.  He passed Dillon for his final lead of the night sixteen laps from the finish and stayed there the rest of the way, notching his third victory of the season and giving J-G-R a sweep of the two 2016 races run on the Newton oval.  Sam Hornish Junior won the front half of the Midwestern twin bill last month.  Jones’ margin of victory over Dillon was three-and-a-half seconds with Elliott Sadler, rookie Brennan Poole and Dakoda Armstrong completing the top five.  Jones started second, jumped past pole sitter Daniel Suarez at the drop of the green flag and led a race-high 154 laps.  Suarez failed to lead a lap and retired with engine failure in the second half of the race, finishing thirtieth.  As a result, he slipped to second in the regular-season standings and is now fourteen points behind Sadler.