three-peat 
North American informal
verb [no object]
Win a particular sporting championship three times, especially consecutively: until somebody beats them in a best-of-seven series, the Bulls rate as the favourite to three-peat...
- The Lakers won't be three-peating unless they come off cruise control for the conference finals.
- He gained national acclaim by three-peating at the World Series of Poker.
- Too bad the NHL doesn't hand out the Stanley Cup in the fall, or the Coyotes would have three-peated by now.
noun [in singular]
A third win of a particular sporting championship, especially the third of three consecutive wins: all eyes were on the 49ers' bid for a three-peat...
- However, a three-peat and four world championships in five years has easily qualified them for dynasty status, especially in this era of the three-tiered postseason.
- With this year's title a seeming certainty for him, you know he'll be back and hungry as ever for a championship three-peat.
- We're only halfway home toward our goal of a three-peat.
Origin
1980s: from three + a shortened form of repeat.