With Tuesday night’s 109-101 win over the Sixers making the Celtics 12-4 since Rajon Rondo tore his right ACL, some have said the team is better without him. But the Celtics say his absence created more of a sense of urgency, which has sparked their rise in the Eastern Conference standings. The Celtics began Tuesday two games from the fourth playoff spot in the Eastern Conference and home-court advantage in the first round, which is stunning considering Boston was 20-23 when Rondo went down and was expected to sink in the second half. “I just think we’re playing better, for whatever reason,” said coach Doc Rivers. “You have all those injuries, you usually go the other way. I just think our guys kind of came together and realized we don’t have a margin of error anymore. “And maybe that’s why. But overall, I think a lot of things happened, too. I think Avery [Bradley] was just coming back, so our defense improved dramatically with him.” Rivers said Bradley’s presence has been critical. The Celtics had improved to ninth in the league in points allowed entering Tuesday night’s game. “When the guy is on the point of the ball putting pressure, it makes everyone else kind of join in, I think that helped,” Rivers said. “I thought our second unit was just about to take off before all the injuries. So they were finding their way. “And with all the new guys, they were starting to get what we’re doing. You rarely see a team go from 23d in the league in defense to [ninth]. That’s hard to do and we did it because I think guys bought in.”