Richardson, 57, of Laguna Niguel, defeated Roy Smethurst, 61, of England, 3 and 2 in one semifinal at The Virginian Golf Club and Abbott, 60, of Napa, beat David Boesel, 55, of Winter Park, Fla., 2 and 1.
The final is Thursday.
Richardson, a two-time low amateur at U.S. Senior Open, was 2 down after four holes against Smethurst, the 2002 British Senior Amateur champion. He made birdie putts of 20 and 10 feet on Nos. 5 and 6 to square the match.
Richardson took the lead when Smethurst, who was attempting to become the first foreign-born champion in the 49 Senior Amateurs, bogeyed the par-3 8th. Richardson did not trail again.
'I'm swinging a little more like I did when I won it in 2001,' said Richardson, who also won the 2001 British Senior Amateur. A hooked drive by Smethurst on 11 resulted in a bogey and gave Richardson a 2-up lead.
Richardson, whose father, John, won the championship in 1987, was not pushed past the 16th in winning his first five matches.
Abbott didn't lead until he made a birdie on the par-4 12th. On the par-5 14th, Boesel used his length advantage to reach the green in two and two-putted for a birdie to square the match.
Abbott won the next two holes and the match when Boesel bogeyed 16 and 17.
In the morning quarterfinals, Richardson beat Bruce Richards, 60, of Bellevue, Wash., who is a member of the USGA Executive Committee, 3 and 2; and Abbott defeated Edward Craig, 60, of Orlando, Fla., 3 and 2.
In the other matches, Smethurst edged 1994 runner-up Bob Hullender, 66, of San Antonio, Texas, 3 and 2; and Boesel, a 1993 U.S. Amateur quarterfinalist, beat Sam Farlow, 56, of Birmingham, Ala., by the same score.
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