The Celtics suffered a memory lapse last night. So it was entirely without coincidence that they suffered a loss. By failing on the plays that were up for grabs, the 50-50 balls, they succeeded in falling to the Trail Blazers, 92-86. It was more than telling, as well, that while the Celts had 19 fast-break points to Portland’s seven, they were outrebounded by their hosts, 47-36. Maybe it was the fact they had scored so easily two nights earlier in Phoenix, frolicking to 113 points in a rout of the Suns, but the C’s certainly didn’t come into the Rose Garden with the same determination. “I just thought, you score one game, and then as a group we came in and thought we were going to be offensive players,” coach Doc Rivers said. “But you’ve got to do the other end, too, and I didn’t think we did that.” The Blazers arrived with seven straight losses, and they were more willing to rumble before a crowd with a heavy Green quotient. They collected 11 offensive rebounds, often at the most opportune times. “Small things, man,” Kevin Garnett said. “Small things.” Garnett was told of Rivers comments, and said, “If that’s Doc’s perspective and that’s what he thought, then that’s him.” Then he proceeded to agree. “I thought when we needed stops, we couldn’t get them,” Garnett said. “I thought when we had the chance to turn the corner, we didn’t turn it. I thought we had opportunities to take advantage of, and eight out of 10 times we didn’t do it.” As for being kicked on the glass and on hustle plays, Paul Pierce nodded.