Associated Press

BOSTON — The Boston Celtics are home, not home free.

Unable to put the finishing touches on the Los Angeles Lakers and wrap up their first championship since 1986, the NBA’s best team since November flew back across three time zones Monday for a Game 6 they were hoping they wouldn’t have to play.

But injuries, another big first-half deficit and a sub-par performance by center Kevin Garnett cost the banged-up Celtics, who lost 103-98 on Sunday in Game 5 at Los Angeles and left Staples Center kicking themselves at the missed opportunity.

‘‘Not what we wanted,’’ coach Doc Rivers said of the team’s stay in Southern California. ‘‘We wanted two more (wins). Obviously, the blanket was that we get to go home, but we really believed that we could win one of these games. We won one and we’ll take it, but that’s obviously not what we want.’’

The Celtics weren’t at full strength for Game 5, missing center Kendrick Perkins with a shoulder injury. Whether he’ll play in Game 6 will be a game-time decision, but Boston expects to have shooting guard Ray Allen available.

He left the arena immediately following Sunday’s game because of a ‘‘health issue’’ with his toddler son, Walker, who underwent medical tests Sunday and Monday. Allen was still at the hospital when the rest of the Celtics arrived in Boston at about 10:30 p.m. EDT Monday, team spokesman Jeff Twiss told The Associated Press.

Allen planned to take an overnight flight so he could play Tuesday night, according to Twiss.

Despite the loss, the tradition-drenched Celtics feel good about their chances of winning a 17th title — on the 17th.

‘‘We’re one up, with two games to go at home,’’ said Paul Pierce, who scored 38 in Game 5.

‘‘It still feels like we have the advantage, and I do feel like we’re the better team.’’

So the 11th installment of Celtics vs. Lakers, the league’s signature rivalry and one of the best in pro sports, has at least one more 48-minute episode.

After a 21-year gap between finals meetings, these teams aren’t quite ready to part company.

Why would they?

Now five games old, this series has had plenty of drama (Pierce’s return from a Game 1 knee injury), history (Boston’s finals record 24-point comeback in Game 4), surprises (Leon Powe’s emergence as a Game 2 star) and even a little scandal as former referee Tim Donaghy’s allegations of fixed playoff games has hung over the finals like a layer of L.A. smog.

The Lakers are trying to become the first team in finals history to overcome a 3-1 deficit to win a title, and they’re one step closer. If they can win Game 6 on Tuesday night in TD Banknorth Garden, they’ll force a decisive Game 7 to cap a season as trying as any in commissioner David Stern’s career.

Kobe Bryant and his teammates staved off elimination Sunday by getting more physical with the Celtics, who Tuesday night will play their 26th game of this postseason — a record — and could be wearing down physically.

Los Angeles center Pau Gasol shed his ‘‘soft’’ label for a night and scored 19 points with 13 rebounds, banging his way inside against Garnett, the league’s best defender who couldn’t push back at the Spaniard while hampered with fouls.

‘‘Pau was terrific,’’ said Bryant, who set the tone early with 15 first-half points and finished with 25 on 8-of-21 shooting. ‘‘He was aggressive. At both ends of the floor he did a great job.’’

Garnett was disgusted by his game and Boston’s big man vowed to make amends when the Celtics get back inside their rowdy house on Causeway Street, where Boston’s fans arrive early, party late and treat visitors with little regard.

Lakers, you’ve been warned.

‘‘It’s going to be like coming into the Amazon, into the jungle,’’ he said. ‘‘I look forward to coming home and playing.’’

Following the teams’ first across-the-U.S.A. trek of the series, Game 3 was one of the sloppiest finals games in recent memory as the Lakers and Celtics battled jet lag and season-ending fatigue.

With just one day off in the highly debated 2-3-2 format, Boston coach Doc Rivers expects Game 6 to be a struggle.

‘‘It’s a terrible turnaround,’’ he said. ‘‘It’s as tough as you can have. I think going West to East is tougher. Sleep patterns are messed up. It’s a tough one. There’s no way around it. But both teams have the same issue, so it could come down to a game of mental toughness, who fights the fatigue mentally better than the other group.’’

But Boston is comforted by being at home, where they are 12-1 in the postseason, where the parquet-patterned floor soothes any nerves and where the 16 championship banners hanging overhead link the Celtics to their past and remind them of their goal.

‘‘That,’’ Rivers said, ‘‘’is not a bad place to be.’’