SANTA CLARA — The 49ers suffer from a rare condition called Third Game Syndrome. They win two games in a row and then they don't win the third. They've repeated this pattern five times this season. They've just notched their sixth two-game win streak, and the third game looms.

Third Game Syndrome (TGS) is the Unknown Factor, the X factor of the 49ers' season. No one can pinpoint the cause of TGS, although some have tried. In their 12 wins, the 49ers beat their opponents by an average of 17.3 points, but in every third game, the 49ers were outscored by an average of 15.2 points.

How can a team play so well for two weeks and so poorly every third game?

Some 49ers dismiss TGS entirely. "We're not really aware of that," Donte Whitner said. "We don't worry about that. It doesn't really matter. I think it's just a coincidence."

Jim Harbaugh chooses to see the positive side to TGS: "(There are) probably quite a few teams that would want that pattern," he said.

He has a point. If you suffer from full-blown TGS, you're winning twice as many games as you're losing, and that's very good. But here's a strange fact: Of the 92 teams to play in the 46 Super Bowls, every one of them had at least one winning streak of at least three games in the regular season. No team with full-blown TGS has ever made the Super Bowl.

If the 49ers beat the Falcons on Sunday, they'll win their third consecutive game and TGS will be history — and good riddance. But if the 49ers lose, people will wonder why they couldn't find a cure.

Let's briefly review every third game of the 49ers' season and see if we can find a common theme.

Week 3 in Minnesota: The 49ers were seven-point favorites. They had just beaten the Packers and the Lions, two playoff teams last season.

The 49ers lost to the Vikings, 24-13, and offensive coordinator Greg Roman called eight runs and 21 passes in the first half.

Week 6 vs. the Giants at home: The 49ers were five-point favorites.

They had just beaten the Jets and the Bills by a combined score of 79-3. The 49ers lost to the Giants, 26-3. Roman called eight runs and 20 passes in the first half.

Week 10 vs. the Rams at home: The 49ers were 11?-point favorites. They had just beaten the Seahawks and Cardinals, the two toughest teams in the NFC West, experts said. The 49ers tied the Rams, 24-24. Roman called 13 runs and 18 passes in the first half.

Week 13 in St. Louis: The 49ers were seven-point favorites. They had just beaten the Bears on Monday Night Football and the Saints in New Orleans. The 49ers lost in overtime to the Rams, 16-13.

Roman called 12 runs and 18 passes in the first half.

Week 16 in Seattle: The 49ers were one-point favorites. They had just beaten the Dolphins and the Patriots in Foxboro and clinched a playoff berth. The 49ers lost to the Seahawks, 42-13. Roman called seven runs and 23 passes in the first half.

Observation 1: The 49ers were coming off big wins.

Observation 2: The 49ers were favored to win each game.

Observation 3: Greg Roman used pass-heavy game plans. Over the season, the 49ers ran more than they passed.

Jonathan Goodwin thinks the 49ers might have been a bit complacent in those games. "Maybe we just kind of got in a lull in the regular season after a little success," he said.

Scott Tolzien elaborated on that. "In college, you have a non-conference schedule and a conference schedule, so you kind of know what your tough games are going to be," Tolzien said. "At this level, they're all tough, and it really is an emotional roller coaster. You win two games and, naturally, you're feeling good about things."

The 49ers feel great about things right now. They just shocked the nation by demolishing the Green Bay Packers and establishing Colin Kaepernick as the most exciting player in the NFL. And now the 49ers are four-point favorites over the Falcons. Almost everyone expects the 49ers to win. They've been in this situation before.

Will the players come out flat in Atlanta?

Will Greg Roman use a pass-heavy game plan? Will the 49ers fall victim to TGS again? Have they finally been cured?