[2] In September of that year, O'Brien made his major league debut with the Red Sox and went 5–1 with a 0.38 earned run average.

[3] In 34 starts and 275 innings pitched, O'Brien won 20 games with a 2.58 ERA and 115 strikeouts; he finished in the top 10 in the American League in all five categories.

Boston eventually took a 3–1 series lead, with ace pitcher Smokey Joe Wood slated to start Game 6.

However, club owner Jimmy McAleer wanted the series to go back to Boston so he could get the gate receipts; he ordered manager Jake Stahl to start O'Brien instead of Wood.

He went 4–9 before being sold to the White Sox, and just one year after winning 20 games, his major league career ended.