UAAP Seasons 81–82: Promising seasons Lastimosa first played for the
Adamson Soaring Falcons in
UAAP Season 81. He debuted with six points, three rebounds, and four assists to help Adamson upset the
Ateneo Blue Eagles. In their rematch with Ateneo, he led the team with 13 points, but Ateneo won over them. That season, Adamson was second in the standings. He rose to prominence as a player when he converted a clutch triple to force overtime against the
UP Fighting Maroons which Adamson survived for a few minutes in the
semifinals. However, they lost their twice-to-beat advantage, and UP moved on the Finals. Lastimosa had more playing time the following season, but still came off the bench for
Val Chauca. In a win over the
UE Red Warriors, he contributed 16 points, eight rebounds, and six assists. Against UP, he had some turnovers and missed a three with 2.8 seconds left in overtime that led to the Adamson loss. In their rematch against NU, he had an all-around performance of 10 points, nine assists, six rebounds, and four steals. He had a costly offensive foul against UP when he stuck out his leg on a three-ball attempt in their final possession, allowing UP to seal another win over them. They were eliminated from playoff contention in a loss to the
FEU Tamaraws. His final averages that season were 8.5 points and 4.1 assists, which was less than what he had expected of himself. He made 11 out of his 14 points in the first quarter, including a three-point shot that gave Adamson a commanding 16–2 cushion halfway through the period that they never looked back from. Against the
UST Growling Tigers, he had a near double-double of 16 points and nine rebounds, but it wasn't enough as UST took the win. In their game against UP, he had 18 points, six rebounds, and three assists but missed the game-winning three pointer as the Falcons lost their third straight. At the end of the first round, Adamson had a record of 1–6. In their second round match against FEU, he led Adamson with 17 points, eight rebounds, and had the game-winning assist to rookie teammate
Matty Erolon, who made the game-winning three. Against NU, he tallied 17 points on an efficient 6-of-8 shooting clip with five rebounds, four assists, a career-high three blocks, and two steals. In their rematch against UP, he hit a clutch three-pointer and two free throws as Adamson got revenge for losing to UP in the first round. He then set a then career-high of 24 points to go with six rebounds, three assists, and three steals. He led all scorers in the league at the end of the two-round elimination that season. He was also in the top five for free throw percentage. The Falcons however, did not make the Final Four. Despite getting offers from
Korean Basketball League (KBL) teams, Lastimosa opted to stay with Adamson for another year. In a win against UE, he had 11 points, seven rebounds, and no turnovers. He dropped a career-high of 29 points when the
Soaring Falcons edged the
De La Salle Green Archers in an overtime win in the first round of
Season 85 on October 22, 2022. In a loss to UP, he had 19 points, three rebounds, three assists and three steals. He didn't finish the game though, as he stepped on the foot of UP guard
JD Cagulangan and had to be subbed out of the game. The injury, which was a dislocated right foot, caused him to miss most of their games in the second round. He returned to playing action against UE. In the next game, he made five of his eight threes for 23 points as Adamson kept its playoff hopes. Against NU, he hit a game-winning three-point shot with 5.5 seconds remaining. He was named co-UAAP Player of the Week along with La Salle's Bettina Binaohan, a women's basketball player. In a do-or-die contest for the last spot in the Final Four, he scored 11 straight points in the third quarter to help the Falcons take the lead against the Archers. He then made two clutch free throws with 12 seconds left in the game as Adamson held on for the win, and got their Final Four spot and a matchup with Ateneo. He finished the game with 22 points (on 4-of-10 shooting from three), and six assists. In their Final Four game against Ateneo, Ateneo's defense limited him to just 10 points on 4-of-15 shooting as Ateneo moved on to the Finals, and their season ended. A UAAP special award—PSBankable Player of the Season—was given to Lastimosa during
Season 85 awarding ceremonies on December 14, 2022 after winning four Player of the Game honors.
UAAP Season 86: Final season Lastimosa continued to play for the team in his final year in
UAAP Season 86. Before the start of the season, his jersey #7 was retired by Adamson, becoming the first Adamson athlete to have that honor. Lastimosa suffered a partial ACL tear in his left knee in the weeks leading up to the start of UAAP Season 86. This caused him to miss the entire first elimination round of the season. He made his comeback in a game against the UP Fighting Maroons on October 25, 2023, but unfortunately suffered another injury to the same knee just eight minutes into the game. Lastimosa was accidentally hit in the knee by UP's
Gerry Abadiano and had to be carried off the court by his teammates. This time, the injury was diagnosed as a full ACL tear. He decided to delay surgery until Adamson's final game of the season. In Adamson's final game of the season, a loss to Ateneo, he ended his collegiate career with a buzzer-beating three-pointer when Ateneo gave away their final possession to give him one more shot. He underwent successful surgery for his torn ACL on December 8, 2023. == Professional career ==