Brazilian midfielder Jorge Wagner's goal enabled Kashiwa Reysol to beat Montedio Yamagata 1-0 as they snatched the lead in the J.League standings.
The only goal came in the 33rd minute after defender Tatsuya Masushima was brought down in the area to give Kashiwa a decisive penalty kick.
Kashiwa now have 59 points, two ahead of previous leaders Gamba Osaka, who lost to defending champions Nagoya Grampus 4-1 yesterday.
Nagoya trail them on 56 points, followed by Yokohama F Marinos on 52 points, Vegalta Sendai on 50 points, and seven-time champions Kashima Antlers on 44 points.
In the only other game today, Brazilian striker Bruno Lopes scored twice to lead Albirex Niigata to a 2-1 win over Kawasaki Frontale.