The 29-year-old Howell had a 14-under-par 130 and fellow Englishman Donald was at 131 after both shot 65 in the second round.
The two front-runners both played on Europe's Ryder Cup team for the first time this year.
McDowell had an even-par 72, 10 strokes higher than his score in the opening round.
"Because of the Ryder Cup there are a number of feel-good factors and I think most guys feel good about themselves at the moment," Howell said, referring to Europe's victory over the United States in the recent cup matches.
"But I am also swinging the club very well just now and hitting lots of good shots, so maybe I am walking a half an inch taller."