Here is the text from the article.
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Lendl Adds Vilas to List, Wins Title in WCT Finale
Ivan Lendl defeated Guillermo Vilas, 7-5, 6-2, 2-6, 6-4, to win yesterday's $250,000 World Championship Tennis winter final at Detroit's Cobo Arena.
The victory was the 62nd straight indoors for Lendl, 22, who last week beat John McEnroe in straight sets for the Volvo Grand Prix title.
Lendl won $125,000, Vilas $40,000.
Lendl, who didn't seem to get into the flow of the match until the fourth set, served seven aces, three in the final set. However, it was his machine-like play along the base line that kept him in contention until he found his serve.
"I was very disappointed because I was missing from the base line, especially in the second set," Lendl said. "It was very frustrating for me."
With the score 2-2 in the fourth set, Lendl broke Vilas' service after going to deuce, winning on two long rallies. Each man won his service the rest of the way, but it was clear that Lendl was the better.
Said Vilas, "When I had my chances I didn't take advantage" . . ."
My thoughts are - you placed other tournaments at 500 level because of prize money, why not this one? I agree, this is all in the realm of opinion.
Thank you for the text of the article you reported to me.
What you collect is ... "the Problem", because it is an anomaly.
You rightly ask me the question: "did you place other tournaments at 500 levels because of the prize pool, why not?"
The WCT since 1982 is the problem, the anomaly because (while before it was part of the ATP / Grand Prix or before 1978 it was not an integral part of the ATP but the circuit was recognized by the ATP) it clearly stands out from ATP / Grand Prix.
The WCT Tour is not considered, no points are awarded for its tournaments, it is not ranked.
Essentially, WCT tournaments are all not-sanctioned.
The main assumption that guides me in trying to understand the various categories of tournaments is mainly the prize money (and ATP score), then the seeding, but always within the ATP / Grand Prix tournaments (we never discussed unreported tournaments).
WCT tournaments after 1982 are essentially not sanctioned (sanctioned only years later, at a later date) and sowing is really low profile.
Detroit is a winter version of Finals of a circuit that practically doesn't exist anymore.
There is a problem with the prize money, in the sense that the WCT tournaments of 1982-83 were very rich, Lamar Hunt had distributed money in explosions for real empty tournaments (the definition that comes to mind is "empty shells" ).
IMHO the inclusion of Detroit for the prize money among the Masters 500 is acceptable (although I disagree).
What risks is inserting all the WCT tournaments won by Lendl in 1982-83 (as done by TenniBase if I remember correctly) because they are rich in prize money, when they are all low-profile.
And in this case, Lendl's career is altered, overestimating it.
Looking back at the WCT titles won by Ivan instead of Detroit, I'd include
Munich and especially
Delray Beach, a good event.
Regardless of your choice to include WCT Detroit 1983 (or other WCT tournaments) between the 500-1000 Masters, your idea of the thread is very good.
The next part of IMHO that would be to identify those that are the real Masters 1000 (which are not those of Wikipedia) and the Masters 500 is more difficult because there were not two types of categories as in the last few years but more.
The roads you have available are substantially 3:
1) identify various categories between 1000 and 500, for example Masters 600, 700, 800, 900 .. but it seems excessive to me;
2) identify 2 categories between 1000 and 500, for example Masters 850 and Masters 700;
3) identify only one category between 1000 and 500: half ... Masters 750.