Williams had 29 points and 12 assists to lead the Brooklyn Nets to a 101-93 victory over the Celtics on Wednesday night.
"Very comfortable," Williams said when asked how he was feeling on the floor. "I was able to attack the rim a lot and get to the free throw line 10 times. That helps build confidence, getting to the free throw line and knocking them down."
Williams went 10 for 10 from the free throw line.
"I think we had good space and gave him room to operate," teammate Jerry Stackhouse said. "Whenever two (people were covering) the ball, he makes the right play. I think once he mixes it up, it's like pick your poison. A lot of times they allowed him to play 1-on-1 and he took advantage of it."
With the victory, the Nets moved closer to wrapping up fourth place in the Eastern Conference and clinching home-court advantage in the first round. Brooklyn owns a 3 ½-game edge over idle Chicago with four games left to play in the regular season.
And if Williams continues to play like he did on Wednesday, the Nets will be very tough in the playoffs.
"We say it every game, he's playing like one of, if not, the elite point guards in the league," interim coach P.J. Carlesimo said.
Boston coach Doc Rivers clearly saw a Nets team that was aggressive offensively, especially when his best defending guard, Avery Bradley, got in foul trouble.
"It's no coincidence that when Avery went off the floor, Deron Williams got ultra-aggressive," Rivers said. "I give Deron a lot of credit; when Avery picked up that first foul he attacked him."
The Celtics, who have dropped four of six, remained three games ahead of Milwaukee for the East's seventh playoff spot, but fell 2 ½ games behind sixth-place Atlanta, which beat Philadelphia 124-101.
"I think we're focusing too much on the playoffs, and that's not here yet," Garnett said. "I think we need to focus and lock in on these games that we have left and put the energy and effort behind that."
Pierce felt the Nets were the more eager team.
"They came in with a better sense of urgency like the playoffs are around the corner, and we sort of eased into it," he said.
Garnett got a technical in the second quarter and tangled up Kris Humphries for a jump ball that had the Celtics' star rolling over the Nets' forward midway into the fourth.
Earlier this season, Rajon Rondo and Humphries were ejected for scuffling under a basket and into the first row of seats after the Nets' big man knocked Garnett to the floor with a hard foul.
The Nets pushed a 10-point halftime lead to 60-45 on Stackhouse's jumper from the right baseline before Boston started to get some production offensively -- mainly from Pierce. After missing six of their initial seven shots in the second half, the Celtics relied on Pierce driving to the basket, where he converted a three-point play and was fouled, hitting five free throws that cut it to 70-62. He had 13 points in the quarter.
But Johnson followed with a 3 from the top, triggering a 7-2 spurt that helped the Nets to a 79-69 lead after three quarters.
The Celtics just had no answer for the penetrating, game-controlling Williams, who made key passes and continually found his way to the basket.
Boston sliced its deficit to nine three times in the opening 6 minutes of the final quarter, but after the last one Williams had a pair of baskets during a game-sealing 8-0 run that had many in the crowd heading for the exits.
Brooklyn hit six from beyond the 3-point line and shot 51.4 percent (19 of 27) in the opening half.
In the opening half, the Nets used a 15-4 run over a five-minute stretch late in the first quarter en route to a 22-21 edge after one. Johnson started the spree by nailing a fadeaway and following Brandon Bass' basket with a 3 from the wing. Boston missed six straight shots during Brooklyn's run.
Then they went on a 18-4 spurt late in the second, turning a two-point deficit into a 12-point lead before Pierce's driving basket in the closing seconds cut it to 53-43 at halftime. Williams had 11 in the quarter, 5 coming in the run.
The teams hadn't played since Boston beat the Nets by 17 in Brooklyn on Christmas Day. "It's different," said Carlesimo, who took over two days after that game when Avery Johnson was fired. "They don't have Rondo and KG (Kevin Garnett) is just coming back." ... Garnett passed Hall of Famer John Stockton for sixth on the NBA's career list in minutes played. ... Pierce and Jason Terry both played their 1,100th career game and Brooklyn's Johnson played his 900th. ... It was the first of three straight on the road for the Nets. They play Indiana on Friday and Toronto Sunday before returning home for their final two games of the regular season. ... The Celtics are off until a matchup in Miami against the Heat on Friday. They play at Orlando on Saturday on Saturday night.