All-Met running back Marcus Whalen rushed for 166 yards and a touchdown as No. 12 Thomas Stone defeated Charles County rival Westlake for the second consecutive week, 41-12, last night in a Maryland 3A quarterfinal in Waldorf.

With the victory, third-seeded Thomas Stone (11-0) advanced to the state semifinals, where it will face No. 7 seed Randallstown. Last week's victory over Westlake had given the Cougars the Southern Maryland Athletic Conference title.

Thomas Stone scored 28 second-half points, and No. 19 Westlake committed four unsportsmanlike conduct penalties and two turnovers in the half.

* GAITHERSBURG 30, OLD MILL 3: Junior Semaj Richardson, usually a reserve, rushed for 192 yards and three touchdowns to lead host Gaithersburg. Richardson came in for leading rusher Jake Colbert, who sat out the 4A playoff game with an ankle injury.

After the Patriots (7-4) took a 3-0 lead on Seth Keil's 37-yard field goal, Richardson scored on runs of 37 and five yards. The Trojans (10-1) held a 14-3 lead midway through the second quarter.

The Trojans made it 21-3 in the third quarter on Ian Hamilton's 32-yard touchdown pass to Norman Smith. Later in the period, Richardson scored his third touchdown, on a 65-yard run.

Colbert is expected to play next week against Severna Park, according to Gaithersburg Coach John Harvill.

* HOWARD 6, MIDDLETOWN 0: Senior defensive end Lewis Matthews returned a fumbled field goal snap 58 yards to give the host Lions a 6-0 win in a 2A playoff game in Ellicott City.

With less than a minute left in the first half and Middletown lining up for a 47-yard field goal attempt, senior nose guard Barry Dagold forced the holder to fumble the snap. Matthews picked up the loose ball and ran for a touchdown.

Howard (10-1) will play in the next round the winner of the game between Dunbar of Baltimore and Edmondson.

Middletown, which turned the ball over six times, ended the season 10-1.

* RIVERDALE BAPTIST 14, POTOMAC SCHOOL 9: In McLean, junior quarterback Marcus Thomas threw for one touchdown and ran for another to lead the visiting Crusaders to victory in the final game of the season for both teams.

Riverdale Baptist, which didn't field a varsity football team last season, is 5-5. Potomac School is 4-5.