Of the Greenwich boys basketball team’s eight regular-season losses, five came by eight points or less, with two of those defeats occurring in overtime. One of those tough overtime losses came against St. Joseph, a game the Cardinals actually gained plenty of confidence from, despite falling short on the scoreboard.

Tuesday, eight days after dueling in a triple overtime thriller, the Cardinals and Cadets met again, this time with the stakes much higher. Like last week’s matchup, Tuesday’s FCIAC Tournament Round of 16 game was a grind-it-out defensive battle, but this time, the Cardinals had the final say.

Senior guard A.J. Barber scored a team-high 15 points and junior backcourt mate James Pilc added 14 points for No. 15 Greenwich, which upset second-seeded St. Joseph, 50-46, in Trumbull. The Cardinals (4-8) advanced to the FCIAC Tournament quarterfinals, where they will visit 10th-seeded Fairfield Warde on Friday at 5 p.m.

“We had a great week of practice,” Barber said. “Everything we’ve been doing has been building up to the playoffs and our final colors are starting to show. We didn’t have our best game, but it was good enough to win.”

Greenwich, which lost to St. Joseph on March 8, 66-58 in triple overtime, had the lead after each quarter of Tuesday’s postseason game. The Cadets (11-2) were held to their lowest point total of the season.

“This St. Joseph team is averaging 74 points per game and they scored 43 in four quarters on our court (before triple overtime) and tonight, our guys just got after it on defense,” Greenwich coach Todd Trimmer said. “We couldn’t make a basket, but it was a great defensive effort by our guys. We’ve been saying it all year, if we can put our defensive effort together for 32 minutes we can beat anybody. I think that we can beat anybody and we showed that tonight.”

As exciting as the victory was for the underdog Cardinals, that’s how frustrating it was for the Cadets. St. Joseph began the season with 11 straight victories, before losing their regular season finale against Staples. Tuesday, the Cadets, normally a high-scoring squad, played most of the game at the Cardinals’ tempo. Greenwich’s mostly man-to-man defense was effective against St. Joseph and it created a good number of second and third shots against the Cadets by hitting the offensive backboards. The Cadets were led by senior guard Tommy Shannon, who scored a game-high 23 points, including five 3-pointers.

“We just couldn’t get over the hump tonight,” St. Joseph coach Kevin Wielk said. “The big shots we were hitting all year just weren’t falling. Or the key stop we needed, we couldn’t get it tonight.”

Senior guard Jason James had nine points and senior guard Glenn Manigault contributed eight for the Cadets, who trailed 21-19 at halftime and 37-33 after three quarters of play.

“Greenwich played a good game,” Wielk said. “They’re well coached, they had a good scouting report and they were ready to play.”

After sophomore guard Dean Brown swished a 3-pointer from the right side to give Greenwich a 25-24 edge with 6:10 remaining in the third quarter, Shannon buried a shot from beyond the arc, then scored on a spin move at the baseline, putting St. Joseph on top, 29-25 with just over five minutes left in the quarter. Pilc converted a 3-pointer from the top of the key, bringing the Cards to within 29-28. Trailing 31-28 following a St. Joseph basket, Barber made a layup off a steal and senior guard Dan Arnold drove to the basket and scored, giving Greenwich the lead for good at 32-31 with 1:18 to go in the third quarter. Barber nailed a 3-pointer with 43 seconds left in the third quarter and Pilc made a left-handed layup in traffic, putting the visitors on top, 37-33 heading into the fourth quarter.

“We were hustling out there on defense, the shots weren’t falling for both teams,” said Arnold, who scored seven points. “We were working hard on defense throughout the game. “Even at the end, we were struggling to inbound the ball, but just getting shots by playing tough defense helped us come out on top.”

The Cards opened up a five-point lead three times during the final quarter, behind a pair of free throws from Pilc and junior forward Chason Barber and an Arnold layup. St. Joseph cut Greenwich’s lead to 46-44 when Shannon converted two foul shots with 2:33 remaining. After senior forward Mason Muir made a free throw for Greenwich, Cadets senior forward Brian Robertson scored off the press-breaker, pulling the home team to within 47-46 with just over one minute left to play.

With the Cardinals passing the ball around the perimeter and taking time off the clock, Pilc saw an opening at the left baseline, drove and scored, giving Greenwich a 49-46 lead with 30 seconds to go. After Greenwich got a defensive stop the ensuing possession, Barber sealed the win with a foul shot in the final seconds.

“It was one of those football style games that we play, everyone stepped up and made some key free throws, some big shots and got some 50/50 balls,” Trimmer said. “We did all the little things that aren’t necessarily fun about basketball, but they win you games.”

Chason Barber scored seven points and grabbed several key fourth-quarter rebounds, while Muir totaled two points and also crashed the offensive boards in key situations. Arnold’s putback and Pilc’s layup gave the Cardinals a 20-16 advantage with 1:08 to go in the second quarter. James made a long 3-pointer in the final minute of the first half, which saw the Cadets trail, 21-19.

“Our seniors have meant a lot to us they put this program back on the map,” Wielk said. “All the credit goes to them, they are the ones that helped this program get going in the right direction. It’s heartbreaking, but it happens, you get knocked off sometimes. It’s why they play the game.”

Up next for Greenwich is an FCIAC quarterfinal-round showdown against Warde in Fairfield. Warde topped No. 7 Danbury, 63-56, in Tuesday’s Round of 16. Indeed, Greenwich enters the game a confident squad.

“St. Joe was one of the best teams in the league, now we we felt like we are playing our best basketball at the end of the season,” Trimmer said. “We got a lot of confidence from the first time we played these guys and it just kind of carried over.”

Added Arnold: “This is just one win, it’s a process. We want to get to the championship, that’s what we’re looking for.”