Sakaguchi, who shares the Yokohama-shod #19 Toyota GR Supra with Yuji Kunimoto, recorded a best time of 1m18.074s around half an hour into the two-hour morning session to top the times by exactly a tenth of a second.
While that was a considerable improvement from the team's best time on the opening day of testing on Saturday, it was still 0.247s shy of the benchmark established by ARTA Honda driver Nirei Fukuzumi.
Ritomo Miyata continued the promising form of the #36 TOM'S Toyota, which runs on Bridgestone tyres, albeit going marginally slower than team-mate Sho Tsuboi had managed on Saturday.
Third-fastest was Daiki Sasaki in the best of the Nissan Zs, the #24 Kondo Racing car, ahead of the two ARTA Honda NSX-GTs, the #16 car of Hiroki Otsu leading the #8 machine of Toshiki Oyu.
Two more Hondas were next up, the Team Kunimitsu (Tadasuke Makino) example leading Real Racing (Nobuharu Matsushita), followed by the Team Impul Nissan of Bertrand Baguette in eighth.
Besides the two Yokohama cars, the only other GT500 runner to improve on Sunday was the #37 TOM'S Toyota, which was ninth-fastest in the hands of sophomore Giuliano Alesi.
As has become traditional in recent years during official testing, the final session began with a dummy race start, with most teams settling into long runs shortly thereafter and not improving on their morning times.
Nissan topped a session for the first time this year courtesy of the #3 NDDP Racing car of Mitsunori Takaboshi with a 1m19.079s.
Makino was second-fastest aboard the Kunimitsu Honda, 0.264s further back, while Hiroaki Ishiura made it three different manufacturers in the top three aboard the Cerumo Toyota.
In the GT300 class, it was the K-tunes Racing Lexus RC F GT3 of Morio Nitta that led the way with a best effort of 1m25.677s in the morning - 0.277s down on the benchmark set by the JLOC Lamborghini team on Saturday.
Second-fastest was the Shade Racing Toyota GR86 GT of Katsuyuki Hiranaka, whose time of 1m25.725s puts the team third across the two days of testing, while Takashi Kogure, who had set the best time on Saturday, was third aboard the #88 Lamborghini Huracan GT3 Evo.
Subaru recovered from a troubled opening day of testing with its BRZ with the sixth-fastest time courtesy of Hideki Yamauchi.
Three-time champion Nitta made it a clean sweep of fastest times with a 1m26.585s in the afternoon session, which like the morning session passed by without any stoppages.
Official pre-season testing continues at Fuji Speedway on March 25-26, before SUPER GT returns to Okayama for the opening round on April 15-16.
Okayama SUPER GT testing times (GT500 class):
Pos. | No. | Team/Car | Drivers | Morning | Afternoon |
---|---|---|---|---|---|
1 | 19 | Racing Project Bandoh/Toyota |
Yuji Kunimoto Sena Sakaguchi |
1'18.074 | 1'20.787 |
2 | 36 | TOM'S/Toyota |
Sho Tsuboi Ritomo Miyata |
1'18.174 | 1'20.657 |
3 | 24 | Kondo Racing/Nissan |
Daiki Sasaki Kohei Hirate |
1'18.191 | 1'20.050 |
4 | 16 | ARTA/Honda |
Nirei Fukuzumi Hiroki Otsu |
1'18.224 | 1'20.484 |
5 | 8 | ARTA/Honda |
Tomoki Nojiri Toshiki Oyu |
1'18.348 | 1'20.197 |
6 | 100 | Kunimitsu/Honda |
Naoki Yamamoto Tadasuke Makino |
1'18.426 | 1'19.343 |
7 | 17 | Real Racing/Honda |
Koudai Tsukakoshi Nobuharu Matsushita |
1'18.613 | 1'20.259 |
8 | 1 | Impul/Nissan |
Bertrand Baguette Kazuki Hiramine |
1'18.693 | 1'20.226 |
9 | 37 | TOM'S/Toyota |
Giuliano Alesi Ukyo Sasahara |
1'18.789 | 1'20.394 |
10 | 3 | NDDP Racing/Nissan |
Katsumasa Chiyo Mitsunori Takaboshi |
1'18.823 | 1'19.079 |
11 | 23 | NISMO/Nissan |
Ronnie Quintarelli Tsugio Matsuda |
1'18.851 | 1'20.149 |
12 | 39 | SARD/Toyota |
Yuhi Sekiguchi Yuichi Nakayama |
1'18.878 | 1'20.086 |
13 | 14 | Rookie Racing/Toyota |
Kazuya Oshima |
1'18.922 | 1'21.175 |
14 | 38 | Cerumo/Toyota |
Yuji Tachikawa Hiroaki Ishiura |
1'19.327 | 1'19.725 |
15 | 64 | Nakajima Racing/Honda |
Takuya Izawa |
1'19.647 | 1'20.263 |