The British and Irish Lions' decisive third Test in South Africa "has huge implications for the future of rugby", says three-time tourist Ronan O'Gara.

A slow-paced second Test drew criticism as have both sides' playing styles, with little flowing rugby from either.

O'Gara says a quality match is needed "for this series to be saved".

The Lions aired frustration at the use of a South African television match official before their opening win and South Africa director of rugby Erasmus fired back with an unprecedented video critiquing the refereeing of the first Test.

The first 40 minutes of the second-Test defeat took 62 minutes to complete because of time taken to make officiating decisions and O'Gara believes it was "worse viewing" than the opener.

"The series is 1-1 and I don't feel any positivity or excitement about this weekend which is startling when you think about who is playing and what's at stake," the La Rochelle head coach said on Rugby Union Weekly.

"It's very easy to understand the aggrievements of supporters because unfortunately there have been very little positive actions on the pitch.

"It is very disappointing because you are talking about the best of the best of the British and Irish Lions against South Africa.

"There has been cynicism, anger and frustration. The rugby needs to be really strong at the weekend for this series to be saved."

Playing like South Africa 'ends up ugly'

Lions head coach Warren Gatland has recognised the need for change after last weekend's 27-9 defeat and has brought six new players into his starting XV.

Hooker Ken Owens, prop Wyn Jones, scrum-half Ali Price, centre Bundee Aki, wing Josh Adams and full-back Liam Williams enter the fray as a number of Gatland's more experienced Lions are cut from the 23.

Taulupe Faletau, Anthony Watson and Owen Farrell - who O'Gara says could have been "key to the series" - have all been dropped for the decider.

Fly-half Finn Russell is on the bench after recovering from an Achilles injury and number eight Sam Simmonds is another attacking replacement as he prepares for his Lions Test debut.

The world champions will be missing talismans Faf de Klerk and Pieter-Steph du Toit, with Cobus Reinach starting at nine and Franco Mostert moving into the back row.

Lood de Jager starts at lock and 37-year-old fly-half Morne Steyn - who sealed the 2009 series with a long-range penalty - is on the bench.

South Africa were forced to defend their playing style after a second Test dominated by physical battles up front and a heavy reliance on kicking.

The Lions tried and failed to match the Springboks in both areas and O'Gara says the squad selection suggests more of the same could be coming from Gatland's side.

"South Africa are building," he explained.

"They will inevitably be better whereas all of a sudden the Lions is almost a split personality - what are we?

"Do we now change our philosophy, change our style and try and exploit the space that is inevitably there?

"Or do we double down on this type of play that we've seen? I think that is what Gatland has done in his selection.

"Finn Russell aside, it indicates to me that he thinks he can get over the line playing that way and I don't think it's the smartest way to get a result, but perhaps it is in the last Test.

"When you try to play the way they [South Africa] play and you don't get results, it ends up pretty ugly."

'Top level has a problem' if there are not more tries

O'Gara says players "become possessed" when they pull on a Lions jersey and if the current crop can put on a performance similar to those that led to the legendary 1997 series win in South Africa, this tour could still end on a high.

The Lions scored just one try in the first two Tests, with Luke Cowan-Dickie crossing in a maul to help them to a 22-17 victory in the opener.

A total of four tries have been scored in the series so far and O'Gara says if there is not more excitement in the final Test the game "is in danger" as it seeks to win over new fans.

"We're looking at the Lions scoring one try from a drive over maul in Test rugby which means that the game at the top level has a problem," he said.

The former Ireland fly-half said the Lions need a "spark" if they are to have any hope of claiming a series win.

"From an attacking point of view, they are not knocking on the door," he continued.

"There is a kick policy going on but you have to have multi-threats at this level if you want to cause problems.

"You don't win big games without scoring tries."

Line-ups

British and Irish Lions: Williams; Adams, Henshaw, Aki, Van der Merwe; Biggar, Price; Jones, Owens, Furlong, Itoje, A Wyn Jones (c), Lawes, Curry, Conan.

Replacements: Cowan-Dickie, Vunipola, Sinckler, Beard, Simmonds, Murray, Russell, Daly.

South Africa: Le Roux; Kolbe, Am, De Allende, Mapimpi; Pollard, Reinach; Kitshoff, Mbonambi, Malherbe, Etzebeth, De Jager, Kolisi (c), Mostert, Wiese.

Replacements: Marx, Nyakane, Koch, Van Staden, Smith, Jantjies, Steyn, Willemse.