Overcoming a 20-point deficit is impressive. Then again, facing a 20-point deficit is problematic in itself.

There were several factors at which to point the finger for the Celtics' 114-105 loss (click here for the full recap), including the effects of a West Coast road trip, the recent thumb injury of Paul Pierce … even the difficulties posed by the high altitude in Denver.

But on Sunday, the Celtics did not show up for the first quarter against the Nuggets. They gave up a season-high 37 points for a period and trailed by 20. Not the best way to start a game on the road and with their captain offensively ineffective.

Not only were the Celtics outscored early on, they were outrebounded. The Nuggets grabbed 11 boards to Boston’s four in the first quarter alone (Denver finished the game with a 41-37 advantage).

While the Celtics deserve credit for fighting back and tying the game in the third, early deficits can’t be tolerated for a team trying to inch its way back to the top of the leader board.

The Celtics know they have to play 48 minutes of basketball. Now it is just a matter of doing it when they go back to Boston. Here are three other things we know as the Celtics return home.

RAY HAS RETURNED

For weeks it was uncertain if Ray Allen would return to the Celtics. After this road trip one thing is clear — Ray Allen is back.

Allen scored a team-high 25 points against the Nuggets to cap off a four-game stretch in which he averaged 21.3 points, five points better than his season average.

After missing the last game before the All-Star break against the Hornets with back spasms, Allen scored 15 points last Tuesday against the Kings. He shot just 1-for-6 from 3-point range as trade rumors continued to buzz.

But by Thursday night against the Lakers, Allen’s place on the Celtics was secure. The trade deadline had passed and he wasn’t going anywhere … except to the basket. He scored a game-high 24 points, including 12 in the third quarter alone, and knocked down 4-of-6 from long-range.

The veteran showed no signs of slowing down just a day later. He shot 9-for-14 from the field to score 21 points against the Trail Blazers. The Celtics were a team-high plus-19 with Allen on the court.

Allen posted 17 points in the first half against the Nuggets on Sunday. He once again was the C's leading scorer with 25. Allen also shot a perfect 5-for-5 from the free throw line, going 9-for-10 in his last four games.

Doc Rivers joked after the Lakers game that the Celtics should threaten to trade Allen all the time. It doesn’t look like any jokes will be needed. Allen continues to prove he is serious about helping the Celtics win.

WORTH THE TRIP

Even though the Celtics leave Denver on a losing note, their time out West has been quite productive. After over a month of inconsistent basketball, the C’s showed promising signs of improvement in just one week. Here is a look back at the trip that has them looking ahead to the second half of the season:

Feb. 16: Celtics 95, Kings 92 

Paul Pierce and Rasheed Wallace scored 17 points apiece as the first and second unit came together to give the Celtics a victory over the Kings. While it wasn’t a blowout over a struggling Kings team, it was a critical win that gave the C’s momentum for the rest of the trip.

Feb. 18: Celtics 87, Lakers 86 

This game was won with defense. The Celtics scored just 11 points in the fourth quarter yet still fended off the Lakers late in the game. Ray Allen scored a game-high 24 points (12 in the third quarter alone) in the win over the Kobe Bryant-less Lakers.

Feb. 19: Celtics 96, Trail Blazers 76 

Allen continued his hot streak (21 points) and Kevin Garnett added 16 in the Celtics' third straight win. Led by 11 dimes from Rajon Rondo, the Celtics dished 20 more assists than the Trail Blazers.

WHAT’S NEXT?

West Coast road trips always are challenging. But the Celtics don’t get a break when they return home, either. There  still are plenty of questions and obstacles the C’s have to address and overcome back in Boston.

The new guy: Their first task will be transitioning Nate Robinson into the rotation. Robinson, who has been fighting a stomach virus, is expected to make his Celtics debut on Tuesday. As if emotions aren’t high enough for a player in his first game with a new team, Robinson will don a Celtics uniform for the first time against his former team, the Knicks.

The captain: From his knee to his foot to now his hand, Paul Pierce is plagued with another injury. Pierce suffered a right thumb sprain during the road trip and was visibly affected on Sunday. He shot 2-for-10 from the field (five points) and, even more uncharacteristically, made just 1-of-4 free throw attempts. Even though Allen and Garnett were impressive on the road trip, the Celtics need the complete Big Three to stay dangerous.

The Cavs: The new-look Cavaliers will roll into Boston for the first time this season on Thursday. As if these matchups aren’t heated enough, the Cavs have lost their last three games. Expect them to be hungry for redemption against the Celtics on national TV.