The longest winning streak in any professional sports may have been Jahangir Khan's 555 consecutive wins in squash from 1981 to 1986. Currently, Esther Vergeer is on a 349-game winning streak in wheelchair tennis since January 30, 2003, which included a streak of 250 consecutive sets won.
A winning streak is not to be confused with an unbeaten streak, where teams can tie as well as win and keep their streak. For example, if a soccer team wins four games in a row, plays a draw, wins three more, plays two draws in a row, and then loses, they had a 10 game unbeaten streak. Their longest winning streak in this sequence was four.
49 wins -- 1952-1956 Rocky Marciano
Note: Rocky Marciano remains the only heavyweight champion in boxing history to retire having won every fight in his professional career.
22 games -- 1948-1949 Calgary Stampeders
Note: The streak only includes the regular season. It was also achieved back when the Stampeders played in the Western Interprovincial Football Union, which later became the Canadian Football League West Division.
25 games -- 1873-1882 Wilhelm Steinitz
88 games -- 1971 - 1974 UCLA Bruins
Note: This streak includes playoff games. Mount Union also holds the record for most consecutive regular season victories, winning 110 games between 1994-2005.
169 games -- 1986 - 1990 North Carolina
20 dual meet wins -- 2000 - 2003 Stanford University
Special note: Since 1980, Kenyon College has won 29 consecutive men's swimming championships, the most total consecutive championships won at any level of sports in the world.
16 matches -- 1999-2001 Australia
21 matches -- 2003 Australia
14 games (tie):
- 1997 Brazil 
Note: Brazil also holds the unbeaten record of 36 games from 16 Dec 1993 to 21 Jan 1996.
- 2003-2004 France 
29 games -- 1971-1973 S.L. Benfica
28 games -- 2007-2008 Dinamo Zagreb
25 games -- 2003-2004 Celtic F.C.
22 games -- 1987-1988 PSV Eindhoven
17 games -- 2006-2007 F.C. Internazionale Milano
15 games -- 1960-1961 Real Madrid C.F.
15 games -- 2005-2006 Bayern Munich
14 games -- 2002 Arsenal F.C.
15 games -- 1997-1998 L.A. Galaxy
Note: This streak was achieved back when the MLS instituted a shootout rule to eliminate tie games. Only one of those wins was achieved through a shootout. This rule has since been abolished by the MLS after the 1999 season.
7 wins -- 2004 Michael Schumacher
504 games -- 1973-2005 Miller Place High School
159 games -- 1919-1925 Passaic High School
151 games -- 1992-2003 De La Salle High School
459 matches -- 1974-2008 Brandon High School, FL
Horse -- 56 races -- 1953-1955 Camarero 
Jockey -- 9 races (tied) -- September 10-12, 1930 Albert Adams and July 30-31, 1993 Tony Black
- 1978 Nancy Lopez
- 2004-2005 Annika Sorenstam
Note: The Giants tied the Pirates in the second game of a doubleheader 1-1 on September 18, 1916. Major League Baseball excludes all games which end in ties from their official statistics. The longest winning streak without ties in Major League Baseball is 21 games, achieved by the Chicago Cubs in 1935.
Note: Hubbell's streak was achieved in 27 games as he also pitched three no-decisions. In baseball, only losing decisions can end winning streaks by pitchers.
5 wins (tie):
- 1971 Richard Petty
- 1971 Bobby Allison
33 games -- 1971-1972 Los Angeles Lakers
21 games -- 2006-2008 New England Patriots
†Pittsburgh tied New Jersey 6-6 on April 10, 1993 to end the regular season. They won an additional three games to start the 1993 playoffs before losing for the first time in 21 games on April 25, 1993 to New Jersey, 1-4.
11 wins -- 1945 Byron Nelson
555 matches -- 1981-1986 Jahangir Khan
Note: This is the longest winning streak in sports history (in number of wins).
Note: Open era winning streaks on different playing surfaces are also recognized. Roger Federer currently holds the record for the longest winning streak on grass courts (65 matches) and hard courts (56 matches), Rafael Nadal currently holds the record for the longest winning streak on clay courts (81 matches), while Ivan Lendl currently holds the record for the longest winning streak on indoor courts (66 matches).
Note: *There is no consensus as to the number of matches that Vergeer has won during her streak as various sources have reported varying tallies.
40 games -- 2005-2008 Sioux Falls Storm, Sioux Falls, SD
Note: This is the longest winning streak in professional team sports history.
25 Cups -- United States
Note: This is the longest winning streak in the sport's history (in years), with 25 successive victories over 152 years.