Under 3.5 will hold at Audi Field on August 19 as conservative setups and key absences trim scoring chances. D.C. United sit 5-5-9 with 24 points and are unbeaten in six matches, and New England are 9-7-3 with 30 points but have lost their last two matches including a 2-1 loss on August 15 and a 2-…