This article is part of a semester-long series on the last decade in Ivy League athletics. To read the first article in the series, click here.

We’ve already broken down the best long-term dynasties in Ivy League sports, and the best individual seasons as well. But there’s nothing that adds to an already dominant season quite like beating your biggest rival.

There are certain matchups in sports where it seems like everything is on the line, every time the two teams face off with one another. In this edition of our Decade in Ivy Sports, we track the most competitive rivalries in the past decade of Ivy sports. This doesn’t just mean the ones with the most passion, or the most history — it’s about the matchups that are almost guaranteed to determine an eventual champion.

No. 6: Columbia-Dartmouth baseball

---

---

Baseball, as one of the most balanced sports in the Ivy League in recent years, has seen five teams win at least one title and none with an average finish worse than 6.1. But it seems like these two schools — neither of which are known as athletic powerhouses — always find a way to play one another in the most vital games. Four times this decade, Dartmouth and Columbia have met in the Ivy League Championship Series, including three straight from 2013 to 2015. Interestingly, Dartmouth tends to dominate the regular season — the Big Green are 16-5 against the Lions in the regular season since 2009, either splitting or winning the season series all 10 times. But it’s Columbia that has a 3-1 mark against Dartmouth in the series that matters most. The one time Dartmouth did beat Columbia, in 2010, the Big Green were led by future MLB pitcher and 2016 MLB earned run average leader Kyle Hendricks.

No. 5: Yale-Cornell men’s ice hockey

---

---

At first glance, these numbers show clear Yale superiority. But Cornell has made this rivalry far more competitive in the past five years. Between 2009 and 2013, Yale was 10-2 head-to-head against Cornell, while also securing the 2013 national title, four Ivy titles to Cornell’s one, and an 11-0 combined scoring margin in the 2009 and 2011 ECAC Championship games. In the time since, though, the Big Red have stopped being the Bulldogs’ little brothers. Since 2014, each team has two Ivy League titles to its name, and Cornell leads the overall head-to-head series, 5-2-3. In perhaps the biggest sign of the suddenly even nature of the rivalry, half of the teams’ 10 matchups over the past five seasons have gone into overtime. This rivalry even extends to the international stage; at the 2018 Winter Olympics, Cornell alum Ben Scrivens represented Canada, while Team USA featured three Yale alumni.

No. 4: Cornell-Harvard women’s ice hockey

Clearly, a look at the Ivy League titles shows how important the regular season games between these foes have been; only once in the past 10 years has neither squad won the championship. But when it comes to facing off in the postseason, this rivalry escalates to another level. Five times in the past decade have Harvard and Cornell battled in some type of playoffs, including the NCAA quarterfinals in 2010, where the Big Red blew out the Crimson, 6-2. Each team has made the national final once, with Cornell losing there in 2010 and Harvard doing so in 2015. As evenly matched as the teams are, though, the Big Red have a clear edge in producing high-level individual talent: five Cornell alumni appeared for the silver medal-winning Canadian national team at the 2018 Olympics.

---

---

No. 3: Penn-Princeton women’s basketball

If our study only consisted of the past five years, this rivalry would undoubtedly be better than any other in the league. Here’s a breakdown of the past five seasons: the two teams have finished first and second in the standings every year, with Penn winning three times and Princeton twice. Penn’s conference record is 60-10, and Princeton’s is 58-12; the next best is Harvard, way down at 45-25. In three of those five years, the teams finished exactly one game apart, meaning their head-to-head series directly determined the league champion. The teams have gone 6-6 against one another, including a 5-5 regular season split and each team fittingly winning one Ivy League championship game against the other. And of those 12 games, some have been true instant classics. For example, Penn’s 62-60 win at Princeton in March 2016 to clinch the Ivy League championship remains one of the finest games in the history of Ancient Eight women’s basketball. The only reason that this rivalry isn’t higher on the list is that everything prior to 2013-14 can’t just be ignored. From 2009 to 2013, Princeton went 10-0 against Penn, and won four Ivy titles to the Quakers’ zero.

No. 2: Penn-Harvard football

If the Ivy League can be said to have “blue bloods” in any sport, Penn and Harvard football fit the bill. Though neither one happens to be the defending champion right now due to Princeton’s stellar 2018 season, that’s the exception rather than the rule. It’s often a near-certainty that this game will determine the Ivy League champion. The winner of Penn-Harvard won at least a share of Ivy title every year from 2007 to 2016 — and, of course, both teams had five wins against the other in that span. This trend doesn't just cover the past decade, but extends to the whole 21st century. Since 2000, only four times has the winner of Penn-Harvard football not gone on to win the Ivy title. And only once in that span has the loser of the game rebounded to win a share of the title, as a result of the three-way tie in 2015. 

This game has been at its best recently, as well. In 2015, wide receiver Justin Watson exploded for 249 total yards and Penn shut out Harvard in the second half, securing a 35-25 upset to snap the Crimson’s 22-game win streak. The following year, under the Friday night lights at Franklin Field, quarterback Alek Torgersen led a two-minute drill for the ages before finding Watson for a tie-breaking touchdown with 15 seconds left to push the Quakers to a 27-14 victory and give Harvard its first Ivy loss for the second straight year.

No. 1: Penn-Princeton women’s lacrosse 

As far as dynasties on the national stage go, there’s no Ivy League sports rivalry quite like this one. It’s nearly impossible to exaggerate just how evenly matched the powerhouses built by Penn coach Karin Corbett and Princeton coach Chris Sailer are. For starters, Penn and Princeton have shared the Ivy title in four of last five years. The last time that neither school won the Ivy League was back in 2005, and the last time that neither made the NCAA tournament was 1997. And as one would expect, when these two play each other, just about everything is on the line. In the past 12 seasons, 2011 was the only time that the regular season head-to-head winner did not win the Ivy title. 

In the past 10 years, Penn is 6-4 against Princeton in the regular season — but because lacrosse is one of the few sports to have Ivy postseason play, fans get treated to even more of this rivalry. Penn is the only team to have qualified for all nine Ivy tournaments, while Princeton has made eight of nine. In those nine years, the teams have met six times, including three times in the Ivy title game. That most recent Ivy championship in 2018 was one of the best games of all: With both teams entering tied for the lead with three all-time Ivy tournament titles each, Princeton edged Penn, 13-10, in a game that included a staggering seven ties after the first goal was scored.