Before Cilic and Nishikori unexpected success, at least one of the top-four -- Novak Djokovic, Rafael Nadal, Roger Federer and Andy Murray -- played the finals of all Grand Slams since 2005.
Zivojinovic, knows as Bobo, was a true entertainer in his days. His Australian Open quarterfinal win over American great John McEnroe in 1985 is still a part of tennis folklore.
Zivojonovic says dominance of the top-four in the last few years made the game predictable, which was not good for the sport.
"World is getting faster and faster, you have sports with more action. If you don't see action, young kids do not like it. They go for extreme sports. Every match is the same. Time to time, you see them doing well. The top-four guys were there for years in Grand Slam finals, so nothing is new. It's getting boring," Zivojonovic told PTI in a chat.
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Bobo, who had a huge serve in his playing days, said Nishikori's success at the US Open has come at a good time, keeping in the mind the huge population of a few Asian regions.
"It's important for tennis that somebody from Japan came all the way, as well as from China, because this part needs results and heroes for the huge populations," the 51-year-old said.
Asked if it was the end of an era with none of the top-four making the US Open title clash, Zivojonovic said tennis needs better athletes in singles in top-10 and not the baseliners.