From 1976-80, the San Francisco Giants won 75 or fewer games each season ... except one. In '78, kind of out of nowhere, the Giants won 89 games and sort of contended for the National League West title. On Sept. 4, they went into a series with their bitter-rival Dodgers just one game back. They promptly lost two games to the Dodgers and then lost 10 of their next 12 to fall out of contention. Still, it was a heck of a run.

What happened to San Francisco in 1978? How did an otherwise mediocre team get into the groove? Well, it did get better pitching, particularly from lefties Bob Knepper and Vida Blue. A 22-year-old Jack Clark had his first excellent season, hitting .306 with 25 home runs, and he finished fifth in NL MVP Award voting.

But it probably came down to something else.

In 1978, the Giants won 42 games by one run.

That's the record, if you are wondering. No other team in baseball history has won 42 one-run games in a single season. This bit of trivia is particularly interesting right now because in the American League West this year, the Mariners are doing something so remarkable, it seems like an optical illusion: They are in first place in the division, entering Tuesday a half-game up on the defending World Series champion Astros, which is crazy on its face. Then you add this little fact: Houston has outscored its opponents by 127 runs. Seattle has outscored its by 22.

How is this happening? Well, you already know: The Mariners have already won an astonishing 21 one-run games. It is the most one-run victories any team has had this early in the season. Seattle is on pace to shatter the Major League mark for one-run victories.

At the same time, the Astros have been terrible in one-run games so far.

The records

Seattle: 21-9

Houston: 6-12

The next logical question is: How do you explain the difference? How can a beat-up team like the Mariners be playing legendary one-run baseball while the defending champs struggle in tightly contested affairs?

Well, what you find with with one-run games throughout history is that they often defy explanation.

How important are one-run games? For more than 100 years, managers have routinely called them the key.

"The team that wins two-thirds of its one-run games," Pete Rose said, "usually wins the pennant."

That overstates the case, but it's true that a freakish year of one-run victories can spark a miracle. Take the 1969 Mets. Nobody expected anything from them. They had finished ninth again in '68 -- they always finished ninth or 10th in a league of 10 teams.

But in mid-April, Tom Seaver beat Bob Gibson's Cardinals, 2-1. The one-run parade had begun. They had a week in which they won two 1-0 extra-inning games with walk-off hits. They had a doubleheader in Pittsburgh where they won both ends by the score of 1-0. They moved into first place on Sept. 10 with a one-run victory. In all, the Mets won 41 one-run games and 100 overall. They went on to win the World Series and to forever be known as the Miracle Mets.

When there's a big surprise team, you often find a crazy one-run record. The 1959 Go-Go White Sox shockingly won the pennant and went 35-15 in one-run games. The 2005 White Sox shockingly won the World Series and also won 35 one-run games. The '84 Padres, the '02 Moneyball Athletics, the '97 Florida Marlins -- these are some of the teams that had a lot of one-run success.

Well, this leads the next obvious question: How do you win more than your share of one-run games? What is the secret? Is there a formula? Great pitching? A dominant bullpen? Fantastic defense? Doing all the little things well? Inspired managing? Team chemistry? The ability to play small ball? Luck?

Unfortunately … nobody really knows. People have been asking that question for more than 100 years. In 1909, one of the great managers of the day, Roger Bresnahan, took over as the skipper of the woeful St. Louis Cardinals. The team had lost 105 games in '08. Bresnahan decided that the path back for the Cardinals was to win the one-run games.

"If a team could win all the games it loses by one run during the season," Bresnahan told his team, "it would be likely to win the pennant in any league."

Bresnahan found what countless managers across all levels have found since: When you focus on winning those tight games, you often end up doing the exact opposite. The Cardinals went an abysmal 16-35 in one-run games and finished 56 games out of first place.

The mystery has continued ever since. In 1951, Billy Southworth -- at the end of what his Hall of Fame career -- quit as manager of the Boston Braves just two months into the season. He quit because he could not get the team to win more one-run games. The Braves had lost 12 of 13 one-run games, and Southworth realized there was nothing he could do.

"There were so many one-run games," he told reporters, "that I decided to quit and let somebody else take over and stimulate the team."

Gene Mauch famously said: "Most one-run games are lost, not won."

The math on that line is questionable, but the sentiment more or less matches that of Bill James, who, as you might expect, has studied the one-run game as closely as anyone. His general takeaway after detailed study was this: "One-run games involve a huge amount of luck."

Yes, they do. The closer the game, the more volatile the possibilities. As a rule, good teams lose more one-run games than normal and bad teams win more. It fluctuates, naturally, but when you look at the greatest teams in history, you find a huge gap between their one-run record and their record in other games.

Here's a short list just to show the point:

1927 Yankees

One run: 24-19 (.558)

Two-plus runs 86-25 (.775)

1939 Yankees

One run: 22-15 (.595)

Two-plus runs: 84-30 (.737)

1955 Dodgers

One run: 21-19 (.525)

Two-plus runs: 77-36 (.681)

1961 Yankees

One run: 29-21 (.580)

Two-plus runs: 80-32 (.714)

1975 Reds

One run: 32-20 (.615)

Two-plus runs: 76-34 (.691)

1986 Mets

One run: 29-20 (.592)

Two-plus runs: 79-34 (.699)

1998 Yankees

One run: 21-10 (.677)

Two-plus runs: 93-38 (.710)

2016 Cubs

One run: 22-23 (.489)

Two-plus runs: 81-35 (.698)

The 2016 Cubs are the best example. They were a dominant team -- their 103-58 record is the best for any World Series team this decade. And yet they had a losing record in one-run games. It just shows the volatility of those tight games. In blowout games, decided by five or more runs, they were a staggering 42-13, one of the best records. Those are easier to figure out. The one-run games remain mysterious.

What about the teams that have had extraordinary one-run records? Is there something that ties them together?

Well, here are the Top 10 one-run records since the Deadball Era:

1. 2016 Rangers: 36-11



2012 Orioles: 29-9

1981 Orioles: 21-7

1970 Orioles: 40-15

1954 Indians: 32-13

1925 Senators: 27-11

1961 Reds: 34-14

1940 Reds: 41-17

1980 Royals: 29-12

1986 Red Sox: 24-10

It's hard to connect the style of play here. The 1954 Indians had one of the greatest starting rotations in baseball history. The '80 Royals got a lot of hits, stole a lot of bases and had a great closer. The 2012 Orioles didn't do much well; they hit a lot of homers and had a manager in Buck Showalter who was widely regarded as a tactical force. The '16 Rangers … I have no idea how the '16 Rangers fit.

The only thing I can find in common is that nine of these teams made the postseason (the 1981 Orioles did not, but that was the strike year). Of the nine, only the '70 Orioles reached the postseason the next year.

I'm not sure there's a whole lot to take from that other than what James said about there being a great deal of luck in winning one-run games.

All of this brings us back to Seattle. It isn't immediately clear why the Mariners have had such freakish success in their one-run games. Their bullpen isn't blowing anybody away. They are tied for seventh in the league in runs scored. Their defense rates below average. And their star, Robinson Cano , is out.

So what gives? Well, they are simply playing better in clutch moments. It's really that simple.

The lineup overall is hitting .256/.320/.418 … middling numbers.

But in high-leverage situations so far this year, they're hitting .290/.349/.494.

That's a gigantic difference; when you look through history, you find that teams almost never hit that much better in the biggest moments of games. But it's true across the board. Mitch Haniger has been only OK in low-leverage situations. But put the pressure on, he is hitting a remarkable .327/.424/.633.

Nelson Cruz scoffs at those numbers. He's hitting .395/.500/.684 in high-leverage spots.

Dee Gordon scoffs at those numbers. He's hitting .213 in low-leverage moments when there isn't much on the line. In high-leverage moments, though, he's hitting .438.

If you were in the prediction business, you would say it's unsustainable. But that's what people said about the 1969 Mets too. Crazy things can happen over 162 games.

Nobody talked more about one-run games than Hall of Fame manager Earl Weaver; he is by some measures the greatest one-run manager in baseball history. He was asked the secret.

"You know how you win one-run games?" he said. "You make the fewest mistakes. You make the most of your opportunities. And mostly, you [bleepin'] score one more run than the other team."