On what may prove to be the most significant day in Super League’s modern history away from the field, Leigh Leopards blew wide open the race for top spot in this year’s competition on it with a stunning victory against the league leaders, Leeds Rhinos.

Super League clubs were finally informed of a long-awaited opening offer from the NRL to invest in the competition on Thursday morning. A figure of around £7m per season, for the next five years, has been tabled but is set to be turned down by clubs – who believe the competition’s value is much higher.

In return, the NRL would take a 10% stake in Super League in each year they invest, but this is likely the first of several negotiations between the two competitions, with some leading figures who were in that meeting telling the Guardian a crucial meeting of the clubs next Thursday will probably lead to Super League rejecting that opening bid.

However, Thursday is still a watershed moment, with expectation high that by the time NRL officials arrive at the end of this month, the two parties will be closer together and able to strike a deal that could revitalise Super League’s prospects, long-term financial picture and potentially its broadcast future.

The NRL are understood to have introduced the broadcaster DAZN into negotiations on Thursday as part of their offer, with Sky Sports – Super League’s longstanding partner since its inception in 1996 – showing three games a week from the start of next year and DAZN potentially picking up the rest. It promises to be a deal that will change how Super League is viewed for ever.

But before then, the competition has a thrilling finale which took another twist here. Leeds had not lost at Headingley all season but the Rhinos came unstuck against one of their main play-off rivals in a thrilling contest, which in turn took the Leopards six points clear of seventh-placed St Helens with just four rounds left. Wigan can now go joint-top with a win against Bradford on Saturday.

The lead changed hands on no fewer than four occasions on the night, but it was ultimately Umyla Hanley’s fantastic try with 25 minutes remaining which proved decisive and gave Leigh a huge victory. That was the only try of an engrossing and high-quality second half, in which the Leopards produced one of their finest defensive displays to deny Leeds.

The Rhinos led after just three minutes when Ryan Hall capitalised on a sublime Jake Connor pass but three minutes later, Leigh levelled through Josh Charnley. Innes Senior finished a magnificent team move from the visitors to put them in front for the first time before Brodie Croft strode through a gap in the Leigh defence to make it 14-10.

By half-time it was level though, as Senior claimed his second to leave it finely poised going into the interval. Connor’s second penalty of the night shortly after the restart put Leeds back in front, but then Hanley responded for the Leopards after a long-range move that caught the league leaders off guard.

There was still 25 minutes on the clock by that stage. But, despite a barrage of attack from Leeds, they couldn’t breach the Leopards’ line again – with a world-class tackle from Hanley to deny Hall in the final minute epitomising how brilliant Leigh were when it mattered most.