Jackson, who earned a 1-up victory over Zahringer at the 2001 U.S. Mid-Amateur, cruised to a 6-and-4 victory in his second-round match over Shawn McCaskey, 33, of Cincinnati, Ohio, and then won in the afternoons third-round action against Gary Wolstenholme, 42, of England, 3 and 2.
'I didnt really hit it as well off the tee against Gary with a couple of flamers to the right but I got it straightened out on the back,' said Jackson, who also won the 1994 U.S. Mid-Amateur. 'Im starting to find out you definitely want to be under the hole and playing to the front edge.'
Jackson will face reigning British Mid-Amateur champion John Kemp, 34, of England, who advanced to the quarterfinals with a 2-and-1 win over Paul Simson, 51, of Raleigh, N.C.
Zahringer, 49, of New York, N.Y., advanced easily through his two matches Tuesday, with a 5-and-4 second-round win over Joseph Taylor, 31 of West Islip, N.Y., and a 6-and-4 victory over Ryan Nierfeldt, 26, of Omaha, Neb., in the third round.
For Zahringer, a member at The Stanwich Club, steady play has been the key.
'I think anything thats even close to par is very competitive,' Zahringer said. 'Thats going to win most of the matches.'
Zahringer quarterfinal opponent will be Austin Eaton, 33, of Stamford, Conn., who made it into the field as an alternate. Eaton cruised in his afternoon match against 1995 Walker Cup player and 1994 U.S. Amateur finalist Trip Kuehne 30, of Dallas, Texas. Eaton never trailed en route to a 5-and-4 victory.
Jerry Courville Jr., 43, of Milford, Conn., birdied the 19th hole to beat Richard Southwick of Shelter Island, N.Y., in the morning action and then earned a 6-and-4 win over David Brown, 41, of Upper St. Clair, Pa.
Courville, the 1995 U.S. Mid-Amateur champion, is attempting to make it into the U.S. Mid-Amateur semifinals for the fifth time. He is currently tied for second with three time champion Jay Sigel for most match play victories, one behind all-time leader Danny Yates.
He will face John Pate, 42, of Santa Barbara, Calif., the older brother of PGA Tour player Steve Pate, who advanced with a 19-hole victory over Greg Reynolds, 55, of Grand Blanc, Mich.
Also advancing to Wednesdays quarterfinals were Jeff Wilson, 39, of Suisin, Calif., and Terrence Miskell, 35, of New Braunfels, Texas.
Play continues Wednesday with the quarterfinal and semifinal rounds. The Championship runs through Thursdays 36-hole final match.
The U.S. Mid-Amateur, for players 25 and older, is one of 13 national championships conducted annually by the United States Golf Association, 10 of which are strictly for amateurs.