Both Harris and McCoy each scored 16 points.
Portageville (12-12) will play top-seeded South Pemiscot for the district championship on Friday at 6 p.m.
"We wanted this game. We really did," Portageville head coach Barry Branscum said. "I thought our girls played with intensity. We're really excited to be in the championship game."
Both teams struggled from the field early on but the Lady Bulldogs (12-12) managed to take an 11-7 lead after the first quarter. Harris scored six of their 11 in the first.
After four minutes of no field goals from either team, Harris finally bucked the trend with 4:34 left in the second quarter to give Portageville a 13-9 advantage.
From there, each team caught fire exchanging nine consecutive baskets. McCoy scored 10 during that span, which included two 3-pointers.
"When (McCoy) gets hot, she's hot," Branscum said. "She kind of had a rough first quarter, but we just told her to keep shooting. A shooter has to keep shooting, even if it's bad."
McCoy's second 3-pointer of the period put the Lady Bulldogs up 23-17 with just over two minutes to play in the half. Buckets by Senath-Hornersville's Reagan Miller, who finished with 10 points, and Taylor Clifton, who led the Lady Lions with 11, cut Portageville's lead to just two, 23-21, at the half.
Although Portageville shot just 37 percent (10 of 27) in the first half, Senath was 9 of 33 (27 percent).
"We got open looks and their defense did a good job of covering," Senath-Hornersville head coach Jaime Johnson said. "If we did get one shot, we didn't get another one."
The second half started much like the first. Each squad traded baskets until Portageville finally broke through.
A steal and a bucket from Senath's Taylor Clifton tied the game at 27. A basket by Harris nearly two minutes later got the Lady Bulldogs going. A steal by Lindsey Young gave Portageville another 4-point lead and from there, the Lady Bulldogs went on an 11-4 run to close out the quarter up 38-31.
"Senath was getting shots but they just weren't falling," said Branscum. "If they hit some of those it's a different game. Quite honestly, we missed a lot of easy shots too that we normally hit. But, we were being challenged by Senath too."
The closest the Lady Lions came to Portageville was five points in the fourth quarter. Senath, who was the tournament's No. 2 seed, reverted to their first half woes shooting 2 of 12 throughout the final eight minutes.
"We played pretty good defense for the most part," Branscum said. "It was probably one of our better defensive games of the season."
Jennifer Ifland added nine points and was a key player under the rim for the Lady Bulldogs who pointed to their rebounding edge as a big winning factor.
"I thought we rebounded extremely well," said Branscum. "When we did give up shots, we rebounded well."
Added Johnson, "I thought they did an outstanding job on the boards. We didn't have any second or third shots."
Senath-Hornersville (12-13) had just four scorers including Clifton and Miller. MaKenzie Crawford added eight points while Rachal Tom chipped in eight as well.
"It was a tough way for us to end the year, but you have to tip your hat to them," Johnson said. "We wish them the best of luck against South Pemiscot. It was a good year for our kids."
Portageville's quest for a district championship will run through South Pemiscot and Carrie Shephard. Shephard led South Pemiscot in their 82-69 win over Hayti earlier on Tuesday.
"South Pemiscot is a fantastic team. They have some players that can do it all," Branscum said. "Carrie (Shephard) is a fantastic player. We have our hands full. We haven't really thought that far ahead because we knew we had to do everything in our power against Senath to win the game."
SENATH--HORNERSVILLE (37) -- MaKenzie Crawford 8, Reagan Miller 10, Taylor Clifton 11, Rachal Tom 8. FG 16 FT 5-8 F 13 (3-pointers: none. Fouled out: none.)
PORTAGEVILLE (49) -- Latavia Harris 16, Jennifer Ifland 9, Taylor McCoy 16, Danielle Morgan 1, Allyson Walls 2, Lindsey Young 5. FG 20 FT 6-16 F 10 (3-pointers: McCoy 3. Fouled out: none.)