Pollard also had eight in the period and Ri'on Lee and Jone' Ayers each had a basket.
All the baskets came on layups and the Millers led 41-24 at the break.
The closest the Vikings got in the fourth quarter was when sophomore Courtney Austin hit a perimeter jumper with 17 seconds left to make it 49-39, but it was too late for a run.
I'm happy to see my team coming together," Milford Mill coach DeToiya McAliley said. "We are not going to win the game by going outside and shooting jumpers, we protect the basket and run the offense."
Lansdowne had a chance to pull away in the first quarter when the Millers missed their first six field goal attempts and committed nine turnovers.
Baskets by Jackson and sophomore Asia Smith gave the Vikings an early 4-0 lead and, after Makayla Pollard made the Millers' first basket, on a putback with 5:15 left, the Millers only trailed 4-2.
But, sophomore Austin sunk a three-pointer and the Vikings led 7-2.
It was the largest lead the Vikings would have all night as the Millers scored seven straight points.
"They were tough and they've got girls that go hard every game," McAliley said. "We weren't playing our game [early] so we had to calm down and play with the basketball."
A fastbreak layup by Mackenzie Pollard, free throw from freshman Janajah Hardison and two fastbreak buckets by Ayers gave the Millers a 9-7 lead before Johnson broke the ice with a free throw and the quarter ended with the Vikings trailing 9-8.
Johnson picked up her third foul with 4:45 left in the second quarter and the Vikings still trailing by one, 15-14.
Milford extended the lead to 21-14 on a 6-0 surge that included three points each from Lee and Dominique Doss.
A basket by Liz McGruder, off a nifty pass from Renwicks (5 assists), cut the deficit to 21-16 with 20 seconds left, but that was the closest they would get the rest of the night.
"I do have to credit Milford," Lansdowne coach Nick Welsh said. "They got up in us and they played very physical so it took us out of our rhythm a little bit. We didn't really seem to get going today."
The Vikings committed 14 turnovers in the first half and they only converted 8 of 24 (33 percent) free throws overall.
They were the second seed in the region after defeating Perry Hall 65-64 in the season finale and earning a first-round bye.
"I thought that we did a great job finishing out the season and we got the bye, but it was almost like a curse — when you get the bye you kind of sit for a little bit too long and you get out of that rhythm," Welsh said. "I just think that having played that day may have kept us a little bit tighter, a little bit crisper."
But, being a high seed wasn't in the conversation last season when the Vikings went 5-15.
"We are an up-and coming program. We are trying to change things and sometimes there are some growing pains, but it takes some time," said Welsh, noting leading scorer Renwicks is the lone senior starter he will lose.
Milford, which won four straight Baltimore County titles until they fell to Catonsville this year, is also young with one senior starter in Lee.
"We have three freshmen, two sophomores and we have a host of juniors," McAliley said. "The seniors don't get a lot of playing time, but they contribute and they are out there so I'm happy to see my team coming together. We are in playoff mode."
Milford Mill 50
Mackenzie Pollard 15, Ri'on Lee 8, Savawn Hughes 8, Jone' Ayers 6, Dominique Doss 5, Janajah Hardison 3, Makayla Pollard 2, Danielle Smith 2, Myah Savage 1