Bjorn Borg's career numbers are as impressive and dominant as those of any other Open Era player but if--following current fashion--the "greatest" discussion must be limited to what we have seen in the past 10 years or so then Rafael Nadal must be included very prominently in that conversation. Nadal defeated David Ferrer 6-2, 6-3, 6-2 to capture his eighth French Open title; he has not only shattered Borg's French Open record (six titles) but Nadal now holds the record for most wins at any single Grand Slam event. Nadal is tied with Roy Emerson for third on the all-time list for Grand Slam singles titles (12), trailing only Roger Federer (17) and Pete Sampras (14). Emerson held that record for more than three decades, but he was not particularly dominant (winning 12 Grand Slam titles in 59 appearances, a .203 winning percentage) and he racked up those championships in no small part because tennis' ridiculous rules during the pre-Open Era prevented Rod Laver and other professionals from playing in Grand Slam events. Emerson won 10 of his 12 Grand Slam titles from 1963-67 without having to face Laver even once; Laver won all four Grand Slams in 1962, was not eligible to participate in the Grand Slam events from 1963-67 and then he won all four Grand Slams again in 1969. Laver enjoyed a 49-18 head to head record against Emerson, who was just two years older than Laver, and Laver won seven of the nine Grand Slam matches that they played against each other.
In contrast to Emerson, Nadal has been dominant (12 Grand Slam wins in 34 appearances, a .353 winning percentage) and Nadal owns a 20-10 head to head record against Roger Federer, who was prematurely crowned by many pundits as the greatest player of all-time. Nadal has never trailed in his matchup with Federer, even when he was a young player while Federer was at the height of his considerable powers. Federer has won 17 out of the 56 Grand Slam events that he has entered (.304) and Sampras won 14 of the 52 Grand Slam events that he entered (.269). Borg still holds the all-time record (11 for 27, a stunning .407 winning percentage). Nadal has now won at least one Grand Slam in nine straight years, breaking the record of eight shared by Borg (1974-81), Sampras (1993-2000) and Federer (2003-10).
Nadal's 2013 season could end up being one of the greatest ever; he has a 43-2 match record this year, including 22 wins in a row. He has won 21 of his 22 matches against top 10 players. It was hilarious to hear some people suggest in 2011 that Nadal had some kind of "Djokovic problem." While Djokovic won all six of his matches against Nadal in 2011, that was clearly an aberration; Djokovic had one great year during which he pretty much beat everybody--including Nadal--but after his five set win over Djokovic in the French Open semifinals Nadal leads Djokovic 20-15 in their head to head encounters and he has never trailed in his head to head matchup with Djokovic. Anyone who thinks that owning a 20-15 advantage over Djokovic is a "problem" for Nadal should explain why Nadal's 20-10 lead over Federer is not a "crisis" for Federer.
Tennis' official ranking system sheds little light on who should be considered the greatest player right now, let alone who is the greatest player of a particular era or the greatest player of all-time; all you need to know about tennis' official ranking system is that, even after Nadal's straight set victory over Ferrer, Ferrer passed Nadal and is now ranked fourth while Nadal drops to fifth. That is why I do not put much credence into who is ranked number one and/or how many weeks a player has been ranked number one during his career; the most relevant tennis statistics are Grand Slam titles won divided by Grand Slam appearances, match winning percentages in Grand Slam events and head to head results against elite players (provided the sample size is large enough), followed by those same statistics in ATP Masters events, followed by those same statistics in all Tour events.
Another important factor to consider is multi-surface dominance; the three most amazing statistics about Borg are that he won over 40% of the Grand Slam events that he entered, that he at one time held the modern record both for career French Open titles (six) and career Wimbledon titles (five) and that he won both of those events in the same year a record three straight times (1978-80). Nadal now owns the French Open record and both Sampras and Federer broke Borg's Wimbledon record but no one has come close to Borg's winning percentage, his French Open/Wimbledon "three-peat" or achieving simultaneous career dominance of both events. If Nadal can stay healthy, he is the one player who could perhaps approach Borg's standards in all of those categories.