Jason Hammond singled to score Duff and Chad Bikle finished the uprising with a two-run double, his second of the game.
Duff had two hits and was the winning pitcher for Williamsport, while closer Spencer Cromer took the loss for South.
Tim Hamilton and Tim Jacobson each had two hits for the Rebels.
No. 1 Jefferson 5, Tuscarora 2
SHENANDOAH JUNCTION, W.Va. - Matt Tiano had a two-run double and Johnathan Hash struck out eight to lead Jefferson (25-3) over Tuscarora.
No. 5 Martinsburg 17, Hedgesville 4
HEDGESVILLE, W. Va - Brandon King was 2-for-4, including a three-run home run in the fifth inning, with five RBIs to lead Martinsburg over Hedgesville.
Jordan Mason also homered for the Bulldogs (20-7). Kaylor Hedges was 2-for-2 with two RBI, Kevin Griffin was 3-for-4 with two RBI, Paul Chenoweth 2-for-3 with two RBI and Zach Newhouse was 2-for-3.
No. 7 Mercersburg Academy 10, McConnellsburg 0
MERCERSBURG, Pa. - Dusty French and Ryan Colby each had a pair of doubles to lead Mercersburg Academy (11-7) to a nonleague victory over McConnellsburg.
St. Andrews 11, St. James 6
SAINT JAMES - St. Andrews scored eight runs in the second inning on the way to a Mid Atlantic Conference win over St. James.
Jimmy Sutch had a pair of hits, including a three-run home run in the fourth inning, and five RBI for the Saints (4-9, 3-7).
Broadfording 7, CVCS 6
Donnie Fritz hit a walk-off solo home run to lead Broadfording Christian past Cumberland Valley Christian in a Mason Dixon Christian Conference game.
Paul Merson struck out 10 and went 3-for-4 with two RBI and Jake Pryor also homered for the Lions.
Southern Fulton 11, Hancock 1
WARFORDSBURG, Pa. - Josh Hall threw a one-hitter and went 3-for-4 with three RBI as Southern Fulton beat Hancock.
Adam Miller had two hits and Derek Younker had two RBI for the Indians (9-4).
No. 1 Hedgesville 15-21, St. Maria Goretti 0-3
Brittany Kolb had four hits as Hedgesville beat St. Maria Goretti in the opener of a doubleheader. Sara Forney had three hits, including two triples, for the Eagles.
In the nightcap, Chelsea Oals had three hits, including a double, as Hedgesville (27-4) completed the sweep of the Gaels (3-15).
Sam Mumaw had two hits and Brittany Kolb homered for the Eagles.
No. 5 Waynesboro 3, Big Spring 1
NEWVILLE, Pa. - Mallory Wishard had the game-winning triple in the top of the 11th inning to lead Waynesboro over Big Spring in a Mid-Penn Capital game.
Taryn Ashway struck out 14 and went 3-for-5 for the Maidens (9-6, 8-2). Emily Master and Amanda Redano each had two hits.
Mercersburg 8, No. 6 Jefferson 7
MERCERSBURG, Pa. - Destiny Hayes drove in the game-winning run in the bottom of the seventh to give Mercersburg Academy the win over Jefferson.
Lauren Dobish had four hits and Cree Riley added three for the Blue Storm (6-8).
Jodi Haynes homered and had two RBI for the Cougars (19-10).
Williamsport 5, South 1
Jessica Bennett threw a two-hitter with 10 strikeouts to lead Williamsport (11-4, 9-3) past South Hagerstown in an MVAL Antietam game at South.
Bri Hammond struck out nine but walked seven for the Rebels (4-10, 3-9).
Southern Fulton 6, Hancock 2
WARFORDSBURG, Pa. - Kelly Elbin struck out eight to lead Southern Fulton (10-3, 5-3) over Hancock.
Kris Creek had two hits for Hancock.
Middletown 18, Smithsburg 6
MIDDLETOWN, Md. - Craig Trueblood had three goals for Smithsburg in a loss to Middletown.
Josh Ritchey, Justin Hovermale and Daniel Rinebolt each had a goal for the Leopards. Trueblood and Ritchey each had an assist.
Catoctin 21, North 3
Katie Bachtell, Devin Zeger and Erin Criswell all scored a goal for North Hagerstown in a loss to Catoctin.
Alex Gomulka had one assist and Neelam Patel had 11 saves for the Hubs.
St. James 16, Highland 5
SAINT JAMES - Caroline Salisbury had seven goals, Gina Clapp added three goals and two assists, and Gina Hontz and Leila Chouai each had two goals as St. James beat Highland.
Anna Morrow and Se-Young Lee each had one goal and Allie Marriott had 13 saves for the Saints.
Middletown 17, Smithsburg 15
MIDDLETOWN, Md. - Cassie Petty had four goals but Smithsburg came up short in its match against Middletown.