Errors played a big part in Canon-McMillan's failure to win its third consecutive WPIAL Class AAAA title last week against Shaler.
And the Big Macs defense cost them again Monday as they started their PIAA championship defense.
Canon-McMillan (18-5) committed five errors for the second consecutive game and lost, 5-4, to DuBois in the first round of the PIAA Class AAAA tournament at Brockway.
The Big Macs trailed, 2-0, heading into the top of the sixth inning. But they got back-to-back home runs from Abby McCartney and Olivia Lorusso, with McCartney's a three-run shot, to take a 4-2 lead.
DuBois cut the deficit to one in the bottom half of the inning, then got a two-run single from Cheyenne McKee in the bottom of the seventh to win.
Canon-McMillan pitcher Tara Fowler was the loser, allowing four hits and two walks in a complete-game effort.
■ Thomas Jefferson 8, Bellefonte 3: Lauren Herazo hit a two-run homer and Tara Conley added a two-run single to help the WPIAL champion Jaguars (16-6) notch a win at Baldwin..
■ Greensburg Salem 2, Warren 0: Melissa Wagner allowed four hits and struck out 12 in a shutout victory for the Golden Lions (17-2) at Penn State Behrend.
■ St. Marys 5, Mars 4: Niki Schlegel went 2 for 3 with an RBI and Blake Kitt drove in two runs in a loss for the WPIAL runner-up Planets (12-6) at Brockway.
■ Beaver 6, Everett 0: Casey Farkasovsky pitched her third shutout in four playoff games, allowing just three hits and striking out seven, to help the WPIAL champion Bobcats (17-0) to a win at North Allegheny. Tayven Rousseau provided the run support, driving in four runs.
■ Bald Eagle Area 2, Seton-LaSalle 1: The Eagles scored the tying run with two outs in the bottom of the seventh then beat the Rebels (13-4) with a walk-off hit in the eighth at Nittany Lion Softball Park at Penn State University. Seton-LaSalle pitcher Lauren Zola got 15 of the first 18 outs via strikeout.
■ Wilmington 8, Deer Lakes 7: The Greyhounds avenged a 2012 PIAA first-round loss to Deer Lakes, scoring four runs in the bottom of the sixth to rally past the Lancers (18-2) at Penn State Behrend.
■ Neshannock 11, Smethport 1: Marissa DeMatteo and Ali Fischer each had three hits and drove in two runs to help the WPIAL champion Lancers (17-2) to a five-inning win at North Allegheny.
■ Burgettstown 6, South Huntingdon 4: Katie Tarr had three hits, including the winning two-run double in the eighth to lead the Blue Devils (18-5) to a win at Nittany Lion Softball Park at Penn State University.
■ Iroquois 10, South Side Beaver 7: Connor McGaffic had three hits, including a two-run home run, and three RBIs in a season-ending loss for the Rams (16-5) at Penn State Behrend.