The 61-year-old woman who tweets on politics and presidents and is scared of nothing is shaking her blonde head and laughing because I've just asked her if she's ever told Roger Federer that this duel he has with Rafael Nadal is, well, comparatively insignificant.

Those guys have played 38 matches, 24 finals, nine of them at Grand Slams. Very nice. But that ain't a rivalry. Not when you're talking to Martina Navratilova. Not when she and Chris Evert duelled 80 times, 60 times in finals, 14 of which were at Grand Slams.

Navratilova, laughing, confesses she has had dinner with Federer a few times and while the Swiss-Spaniard struggle is of course "a huge rivalry" she did add that "Chris and I played 80 times, that will never happen again".

It was a unique tennis duet, it was a singular sisterhood, it was baseliner versus volleyer which turned into a friendship and a book called The Rivals and is a subject which still has people stopping her during her travels and saying: "We miss those days with you and Chris playing". Fortunately they played in a time when people still spoke in full sentences, so no one called them NavErt.

Rivalries didn't die with Martina-Chris because subsequently Monica Seles grunted at Steffi Graf (5-10), Venus Williams versus Martina Hingis (10-11) got heated and Serena versus Justine Henin (8-6) was broadsword versus foil. But then Serena subdued every hopeful coup, had a hypothetical rivalry with Maria Sharapova (19-2), became a mother and left us with a relatively young playing group who can barely hold onto their own form let alone regularly disrupt someone else's.

Women's tennis right now has no rivalry and it needs one because nothing gives a sport a jolt of emotion and a frisson of delight more than two colliding egos and jostling talents. These duets get turned into films (James Hunt, Niki Lauda in Rush), are acclaimed in books (Nicklaus and Palmer in Arnie and Jack by Ian O'Connor) and are so intense that 36 years after their last match there is a movie out this year called Borg McEnroe. And they only played 14 times: 7-7, but of course.

Rivalries are dark, mean, raw, they're challenging, inspiring, illuminating, they bring out a sportsman's best game and their worst side. Said chess genius Bobby Fischer before he played Boris Spassky in 1972: "I have been chosen to teach the Russians some humility."

Fans want face-offs and diversities of skill, they want sulks and obsession, they want contrasts like Federer-Nadal, Sampras-Agassi and Martina-Chris. Because every time there's a clash of playing philosophies it advertises the entire beauty of tennis.

Says Navratilova: "To really get people interested there needs to be some emotion, where people get behind one player over another, so they can follow that player... With the women right now it's been so diluted that the rivalry is missing. Maybe (Victoria) Azarenka, Serena was coming up that way but then Azarenka got pregnant and Serena got pregnant." Then she sighs dramatically and laughs: "Ah, too many babies."

The more consistent today's players become, the more healthy they stay, the more often they collide in finals, the more tension and argument they will create. Navratilova relished Henin v Serena because it was a 50-50 proposition and "that's what makes a rivalry a rivalry - when you're not really sure who is going to win on a given day".

Rivalries can lead to ugliness and not for nothing did Mark Kram give his book Ghosts Of Manila the subtitle The Fateful Blood Feud Between Muhammad Ali and Joe Frazier. But they can also lead to friendships (Larry Bird-Magic Johnson) and acts of generosity (boxer Max Schmeling paid part of rival Joe Louis' funeral expenses) and simply provoke athletes to play better.

As Navratilova explains, Evert was No. 1 and she wasn't and so, she says: "I knew I needed to get to No. 1, and for that I needed to beat Chris, and for that I needed to do some things a lot better. I wasn't going to beat her consistently if I played the same way, so I did train for that. I knew I needed to be in better shape, I needed to improve my serve, and I needed to be more consistent."

This is what the WTA Tour needs now: a chase and a contrast. In the older days it was easier because baseliner versus serve-volleyer was a clear clash of dialects. Now players own too much similar playing DNA, but you can still build some form of rivalries between athletes who play primarily from the back.

Maybe Karolina Pliskova and Garbine Muguruza will bicker like big bullies with their strokes for years, Maybe Jelena Ostapenko and Simona Halep will become a terrific tale of flamboyance versus prudence. Maybe, as we wait, someone will wise up and turn the rivalry of these iron ladies of the 1970s-80s into a film? "It would be fun," said Navratilova. No, it would be fitting.