Suntory Sungoliath ensured they will top the Japan Rugby Top League's Red Conference when the regular season comes to an end next weekend after they beat Kobe Kobelco Steelers 24-7 on Sunday at Prince Chichibu Memorial Rugby Ground.

Wallabies back-row forward Sean McMahon marked his Top League debut with a try and compatriot Matt Giteau weighed in with a five-pointer, three conversions and a penalty goal.

"He has only been with us a week but adjusted really well," Suntory coach Keisuke Sawaki said of McMahon, who joined the club six months earlier than planned following an injury to George Smith.

"When you saw Sean and Matt training together you can really see their hunger."

The result means Kobe cannot finish in the top two and will playoff for fifth to eighth spot in the league.

This season the league has been split into two conferences of eight teams.

Teams play the seven other sides in their conference plus six from the other group to determine the rankings for the end of season playoffs, with the top four sides competing for the league title, which doubles as the All-Japan Championship.

There are three other playoff blocks to determine fifth to 16th positions, with the bottom side automatically relegated.

Toshiba Brave Lupus kept alive their hopes of a top-two finish with a 51-14 drubbing of Kintetsu Liners, their seventh straight win that left them on 38 points, four behind second-placed Toyota Verblitz.

The Brave Lupus play Suntory next week while Verblitz take on Kobe.

Suntory will then play Yamaha on Jan. 6 in the playoffs, which double as the All-Japan Championship, after Jubilo secured second spot in the White Conference.

Panasonic, which secured top place in the white group last week, hammered Ricoh 50-7 to ensure the Black Rams could not overtake Yamaha.

Rikiya Matsuda and Ryu Koliniasi Holani both touched down twice for the Wild Knights, who have bagged 59 points from a possible 60.

Meanwhile at the bottom end of the rankings, Kubota Spears beat Coca-Cola Red Sparks 12-5. The Spears are currently sixth in the red group while Cola is eighth in the White Conference.

In a game it had to win, Kobe started brightly with Takeshi Kizu rumbling over in just the third minute following a well-constructed driving maul.

Codey Rei added the extras from out wide despite a difficult swirling wind.

Things were all square though 10 minutes later, when McMahon powered over following a superb angled run by Hendrik Tui that breached the Steelers' defense.

Giteau added the conversion and then took control of the game as he created a try for Shota Emi, scored one himself following a powerful run by McMahon, and kicked a penalty and two further conversions as Suntory led 24-7 at the break.

"We didn't start well but adjusted our mind set during the course of the game," said Sawaki.

Kobe showed a lot more steel in the second half, camping itself in the Suntory 22 for most of the stanza. But the Sungoliath defense refused to wilt and the 40 minutes concluded with not a single point being scored.

"We didn't start well but showed a lot of patience in defense in our 22," said Suntory captain Yutaka Nagare.

Kobe coach Jim McKay, meanwhile, was left to rue what might have been.

"We played some really good rugby but just couldn't get the scoreboard ticking over," he said.

"We defended well but one or two errors gave Suntory their opportunities and they capitalized and that allowed them to get ahead."